Adds basic emoji index and search by name/unicode.

* Adds index.json from phantom_open_emoji as basic set meta-data
* Adds Emoji::Index class that returns emoji as a hash of string attributes
* Add index lookups by name and 'moji' unicode character
Adds basic rvmrc and fix rake test test_files inclusion.
Adds Emoji lookup APIs and config

* Emoji.image_url_for_name
* Emoji.image_url_for_unicode_moji
* Config via asset_host/asset_path params for URL generation
API for replacing Unicode moji w/ emoji img tags

* `Index.unicode_moji_regex` matches all known moji
* `Emoji.replace_unicode_moji_with_images` escapes any markup in string and then replaces unicode moji with img tags pointing to proper moji image_url
Handle html_safe input/output with escaping.

* Escape strings not marked html_safe?
* Mark outgoing strings html_safe

* Introduces mocha as a dev dependency
* Verify `html_safe?` checking/escaping
* Verify output marked `html_safe`
Update README.md

* Usage examples and config
* Bundle/test callouts
Replace original assets w/ 64x64 rendition and drop retina
Cleanup from code reviews

* swap class variables for class instance variables.
* switch index instance to class instance variable