Add a title attribute to lexers

The title is meant to be a human-readable name for the language. i.e. C++
instead of cpp. When the gem is initialized the titles are all set to the ivar
@title. If no title is set, it will use the demodulized class name:
Rouge::Lexer:XML will become "XML".
Name should fallback to `tag.capitalize`

`demodulize` is not available in plain ruby, only ActiveSupport
Rename viml to VimL
Merge pull request #215 from edwardloveall/el-humanized-lexer-names

Add a title attribute to lexers