documentation overhaul (#353)

* ident
* remove $Id$ tags from rcs software which has been retired
* make an effort to sync required mib docs with actual code
* sync even more docs with what code actually does
* some whitespace nits
* fixup example to use snmpv2 for all but the most ancient devices
* remove blurb to find more specific snmp::info classes for classes
  which alrdy are as specific as they can get (eg snmp::info::layer3::vmware
  doesn't need info on to find a specific module since there ain't none)
* rename all sub {vendor} strings to lowercase vendor, if cisco, juniper
  and arista can be lowercase, so can be all the rest.
* fix tests
* spread some use warnings around
* use $ instead of @
* remove defines that are included via parent classes
* use strict + warnings
* remove alrdy included modules
* add comma after last list item
* typos
* mibs are found in our mib repo, not on the cisco site
* documentation fixes

lib/SNMP/Info/Layer3/Nexus.pm

@@ -55,7 +55,7 @@ $VERSION = '3.68';
 %MIBS = (
 	%SNMP::Info::Layer3::CiscoSwitch::MIBS,
 	'CISCO-ENTITY-VENDORTYPE-OID-MIB'   => 'cevMIBObjects',
-    'CISCO-CONTEXT-MAPPING-MIB'         => 'cContextMappingMIBObjects',
+  'CISCO-CONTEXT-MAPPING-MIB'         => 'cContextMappingMIBObjects',
 );
 
 %GLOBALS = (