Issue 143 - Provide a search rubygems option to load custom rules from a gem.

- Added search for ruby gems option -G (or --search-gems)
- If option is given then search gems for foodcritic/rules/**/*.rb and add these to the
  list of files loaded by the RuleDsl.
Issue 143 - Only use latest gems when searching for rules files.

- Also added some specs for rule file loading.
Include docs and LICENSE in the gem
Include tests in gem too
Merge remote-tracking branch 'rally/issue-143'
Merge remote-tracking branch 'stefanor/include-docs-in-gem'