VPP-57 Add Doxygen to VPP

- Configures Doxygen.
- Adds a source filter to do magic on our use of the preprocessor to do
  constructor stuff to make Doxygen grok it better.
- Adds a convenience helper to the root Makefile.
- Adds a README.md to the root directory (and which Doxygem uses as its
  "mainpage".
- Add several other documentative files.
- Currently using SVG for call graphs, though this may have a
  load-time performance impact in browsers.

Change-Id: I25fc6fb5bf634319dcb36a7f0e32031921c125ac
Signed-off-by: Chris Luke <chrisy@flirble.org>
diff --git a/doxygen/layout.xml b/doxygen/layout.xml
new file mode 100644
index 0000000..e91f4da
--- /dev/null
+++ b/doxygen/layout.xml
@@ -0,0 +1,194 @@
+<doxygenlayout version="1.0">
+  <!-- Generated by doxygen 1.8.11 -->
+  <!-- Navigation index tabs for HTML output -->
+  <navindex>
+    <tab type="mainpage" visible="yes" title=""/>
+    <tab type="pages" visible="yes" title="" intro=""/>
+    <tab type="modules" visible="yes" title="" intro=""/>
+    <tab type="namespaces" visible="yes" title="">
+      <tab type="namespacelist" visible="yes" title="" intro=""/>
+      <tab type="namespacemembers" visible="yes" title="" intro=""/>
+    </tab>
+    <tab type="classes" visible="yes" title="">
+      <tab type="classlist" visible="yes" title="" intro=""/>
+      <tab type="classindex" visible="$ALPHABETICAL_INDEX" title=""/>
+      <tab type="hierarchy" visible="yes" title="" intro=""/>
+      <tab type="classmembers" visible="yes" title="" intro=""/>
+    </tab>
+    <tab type="files" visible="yes" title="Source">
+      <tab type="filelist" visible="yes" title="Files" intro=""/>
+      <tab type="globals" visible="yes" title="Symbols" intro=""/>
+    </tab>
+    <tab type="examples" visible="yes" title="" intro=""/>
+  </navindex>
+
+  <!-- Layout definition for a class page -->
+  <class>
+    <briefdescription visible="yes"/>
+    <includes visible="$SHOW_INCLUDE_FILES"/>
+    <inheritancegraph visible="$CLASS_GRAPH"/>
+    <collaborationgraph visible="$COLLABORATION_GRAPH"/>
+    <memberdecl>
+      <nestedclasses visible="yes" title=""/>
+      <publictypes title=""/>
+      <services title=""/>
+      <interfaces title=""/>
+      <publicslots title=""/>
+      <signals title=""/>
+      <publicmethods title=""/>
+      <publicstaticmethods title=""/>
+      <publicattributes title=""/>
+      <publicstaticattributes title=""/>
+      <protectedtypes title=""/>
+      <protectedslots title=""/>
+      <protectedmethods title=""/>
+      <protectedstaticmethods title=""/>
+      <protectedattributes title=""/>
+      <protectedstaticattributes title=""/>
+      <packagetypes title=""/>
+      <packagemethods title=""/>
+      <packagestaticmethods title=""/>
+      <packageattributes title=""/>
+      <packagestaticattributes title=""/>
+      <properties title=""/>
+      <events title=""/>
+      <privatetypes title=""/>
+      <privateslots title=""/>
+      <privatemethods title=""/>
+      <privatestaticmethods title=""/>
+      <privateattributes title=""/>
+      <privatestaticattributes title=""/>
+      <friends title=""/>
+      <related title="" subtitle=""/>
+      <membergroups visible="yes"/>
+    </memberdecl>
+    <detaileddescription title=""/>
+    <memberdef>
+      <inlineclasses title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <services title=""/>
+      <interfaces title=""/>
+      <constructors title=""/>
+      <functions title=""/>
+      <related title=""/>
+      <variables title=""/>
+      <properties title=""/>
+      <events title=""/>
+    </memberdef>
+    <allmemberslink visible="yes"/>
+    <usedfiles visible="$SHOW_USED_FILES"/>
+    <authorsection visible="yes"/>
+  </class>
+
+  <!-- Layout definition for a namespace page -->
+  <namespace>
+    <briefdescription visible="yes"/>
+    <memberdecl>
+      <nestednamespaces visible="yes" title=""/>
+      <constantgroups visible="yes" title=""/>
+      <classes visible="yes" title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <functions title=""/>
+      <variables title=""/>
+      <membergroups visible="yes"/>
+    </memberdecl>
+    <detaileddescription title=""/>
+    <memberdef>
+      <inlineclasses title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <functions title=""/>
+      <variables title=""/>
+    </memberdef>
+    <authorsection visible="yes"/>
+  </namespace>
+
+  <!-- Layout definition for a file page -->
+  <file>
+    <briefdescription visible="yes"/>
+    <includes visible="$SHOW_INCLUDE_FILES"/>
+    <includegraph visible="$INCLUDE_GRAPH"/>
+    <includedbygraph visible="$INCLUDED_BY_GRAPH"/>
+    <sourcelink visible="yes"/>
+    <memberdecl>
+      <classes visible="yes" title=""/>
+      <namespaces visible="yes" title=""/>
+      <constantgroups visible="yes" title=""/>
+      <defines title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <functions title=""/>
+      <variables title=""/>
+      <membergroups visible="yes"/>
+    </memberdecl>
+    <detaileddescription title=""/>
+    <memberdef>
+      <inlineclasses title=""/>
+      <defines title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <functions title=""/>
+      <variables title=""/>
+    </memberdef>
+    <authorsection/>
+  </file>
+
+  <!-- Layout definition for a group page -->
+  <group>
+    <briefdescription visible="yes"/>
+    <groupgraph visible="$GROUP_GRAPHS"/>
+    <memberdecl>
+      <nestedgroups visible="yes" title=""/>
+      <dirs visible="yes" title=""/>
+      <files visible="yes" title=""/>
+      <namespaces visible="yes" title=""/>
+      <classes visible="yes" title=""/>
+      <defines title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <enumvalues title=""/>
+      <functions title=""/>
+      <variables title=""/>
+      <signals title=""/>
+      <publicslots title=""/>
+      <protectedslots title=""/>
+      <privateslots title=""/>
+      <events title=""/>
+      <properties title=""/>
+      <friends title=""/>
+      <membergroups visible="yes"/>
+    </memberdecl>
+    <detaileddescription title=""/>
+    <memberdef>
+      <pagedocs/>
+      <inlineclasses title=""/>
+      <defines title=""/>
+      <typedefs title=""/>
+      <enums title=""/>
+      <enumvalues title=""/>
+      <functions title=""/>
+      <variables title=""/>
+      <signals title=""/>
+      <publicslots title=""/>
+      <protectedslots title=""/>
+      <privateslots title=""/>
+      <events title=""/>
+      <properties title=""/>
+      <friends title=""/>
+    </memberdef>
+    <authorsection visible="yes"/>
+  </group>
+
+  <!-- Layout definition for a directory page -->
+  <directory>
+    <briefdescription visible="yes"/>
+    <directorygraph visible="yes"/>
+    <memberdecl>
+      <dirs visible="yes"/>
+      <files visible="yes"/>
+    </memberdecl>
+    <detaileddescription title=""/>
+  </directory>
+</doxygenlayout>