Change ruby::version API to add env, remove cc and conf_opts

Adding a bunch of one-off parameters to satisfy an inherently general
configuration problem seems a bit silly in retrospect. Using Puppet's
hashes seems like a fine use-case for this.

Requires a major version bump due to API breakage, though most uses
should be unaffected for 1.9.3 or later versions of Ruby.
Fix gitignore
Add ruby::ree
Always sort environment keys so ci is consistent
Make ruby::gem take ensure and pass it to rbenv_gem
Prefer the rbenv-gem-rehash rbenv plugin over rbenv-autohash gem
Bump boxen and repository reqs
lint
deprecate old homebrew migration path