vppapigen: support per-file (major,minor,patch) version stamps

Add one of these statements to foo.api:

  vl_api_version 1.2.3

to generate a version tuple stanza in foo.api.h:

/****** Version tuple *****/

vl_api_version_tuple(foo, 1, 2, 3)

Change-Id: Ic514439e4677999daa8463a94f948f76b132ff15
Signed-off-by: Dave Barach <dave@barachs.net>
Signed-off-by: Ole Troan <ot@cisco.com>
diff --git a/src/vnet/unix/tap.api b/src/vnet/unix/tap.api
index d9fba37..6b1b2b4 100644
--- a/src/vnet/unix/tap.api
+++ b/src/vnet/unix/tap.api
@@ -19,6 +19,8 @@
     the Linux kernel TAP device driver
 */
 
+vl_api_version 1.0.0
+
 /** \brief Initialize a new tap interface with the given paramters 
     @param client_index - opaque cookie to identify the sender
     @param context - sender context, to match reply w/ request