Group API methods into modules.

As per suggestion by @fhocutt, https://www.mediawiki.org/wiki/API:Client_code/Evaluations/MediaWiki-Gateway. Related to #66.
Remove simplecov dependency.
Remove rr dependency.

Unused since afffb58.
Remove debugger dependency.
Remove atomic dependency.

Unused? Reported as missing in #52 (436cae2).
Swap out builder dependency (via activemodel) for nokogiri.

`nokogiri` also used by `equivalent-xml` and may replace `rexml` in the future.
Swap out activemodel dependency for equivalent-xml.
Remove activesupport dependency.

Use `unicode` or `activesupport` for Unicode support if available.
Remove support files for managing Ruby versions.

We generally default to the latest stable Ruby.
Remove Bundler files.
Swap out jeweler dependency for hen.
Hooking up Travis CI.
lib/media_wiki/utils.rb: Turn into proper module.
spec/utils_spec.rb: Skip UTF-8 example if no Unicode support.
spec/: File hierarchy should match module hierarchy.
spec/: A little cleanup.
spec/: Added data directory and helper.
spec/fake_media_wiki{/* -> }.rb: Joined into single file.
spec/: Added example group alias for fake wiki.
spec/: File hierarchy should match module hierarchy -- pt. 2.