Improved small-tsu substitution in _romajiToKana

I added a check to determine which type of small-tsu should be returned when double-consonants are detected (ッ for KATAKANA, っ for hiragana). I only modified the CoffeeJS script, I didn't set up CoffeeJS to compile the actual Javascript. This is my first foray into CoffeeJS, and I just dove into the code and tried to follow the syntax - I apologize if it doesn't jive with the rest of the code.

You can see what I'm talking about if you go to http://wanakana.com/ and type "NEKKU". You'll see that it returns "ネっク" instead of "ネック". This revision should fix that.
![wanakana_bug](https://f.cloud.github.com/assets/5166470/1405233/57772376-3d20-11e3-8215-79e8a8c1796c.png)