Add minimal Emoji support

[nark]

I'm working on some NLP related stuff with Ruby, and I found the sentimental gem very useful. In my case I have to deal with Emojis, which is today a major way to express feelings in text-based communications.

I tried to catch Emoji unicode symbols with sentimental out-of-the-box (using load_senti_file) but the current regular expressions implementation was kicking unicode out of the tokenized words.

So I updated the regex based on what I found here and I added a emojis.json dictionary with the most common and manful emojis.

I still have to test it more heavily, but currently it perfectly suits my needs.

[jemminger]

Nice! I'd like to see the Emoji regex extracted to a constant so extract_words is more succinct

[OmerGeva]

I think a lot of emojis can be interpreted in different ways, so for example 😂 can be used as a positive or sarcastically negative response. This makes interpreting emojis' sentiments pretty challenging.

Also, 🤡 generally is used in a negative way 😅