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

xt/lib/Test/SNMP/Info/Layer2/Aironet.pm

@@ -122,7 +122,6 @@ sub description : Tests(4) {
 
   $test->{info}{_description} = undef;
   $expected = 'Cisco Aironet 1240 Series (IEEE 802.11a/g) Access Point';
-  $expected .= '  ';
   is($test->{info}->description(), $expected, q(Description is expected value just using Entity MIB));
 
   $test->{info}->clear_cache();