Comprehensive spelling/typo fixes.

Thanks to Josh Soref for generating these fixes.
diff --git a/doc.html b/doc.html
index 54f59bb..26ae731 100644
--- a/doc.html
+++ b/doc.html
@@ -18,7 +18,7 @@
 
 <P>
 The DNS subsystem provides a local DNS server for the network, with forwarding of all query types to upstream recursive DNS servers and
-cacheing of common record types (A, AAAA, CNAME and PTR, also DNSKEY and DS when DNSSEC is enabled). 
+caching of common record types (A, AAAA, CNAME and PTR, also DNSKEY and DS when DNSSEC is enabled). 
 <DIR>
 <LI>Local DNS names can be defined by reading /etc/hosts, by importing names from the DHCP subsystem, or by configuration of a wide range of useful record types.</LI>
 <LI>Upstream servers can be configured in a variety of convenient ways, including  dynamic configuration as these change on moving upstream network.