Extracted RR and RRSet classes from resource and put them in their own files.
Move CodeMapper subclasses out of dnsruby.rb and into code_mappers.rb. Extract Resolv from dnsruby.rb and put in resolv.rb.
Merge branch 'master' into refactor-resource

Conflicts:
	lib/dnsruby.rb
Add comment to dnsruby describing CodeMapper subclasses found in code_mappers.rb.
Merge pull request #33 from keithrbennett/refactor-resource

Relocate CodeMapper subclasses, Resolv, RR, and RRSet classes.