Fixed emoji to text conversion for emoji not surrounded by whitespace

[ckw017]

Fixes this issue: Not predicting sentiment of emoticons correctly #56

Since the current method splits up the text into tokens by whitespace, it won't recognize multiple emoji in a row without whitespace, ie "😀😀😀" isn't given any meaning since the exact string "😀😀😀" isn't in the emoji lexicon, when it should probably have the same meaning as "😀 😀 😀". By checking for emoji on a character by character basis should fix this. Example output after the fix:

>>> SIA.polarity_scores("💋")
//(Interpreted as "kiss mark")
{'neg': 0.0, 'neu': 0.263, 'pos': 0.737, 'compound': 0.4215}
>>> SIA.polarity_scores("💋💋💋")
//(Interpreted as "kiss mark kiss mark kiss mark")
{'neg': 0.0, 'neu': 0.263, 'pos': 0.737, 'compound': 0.8126}

The compound score goes up as expected for three emoji in a row

[cjhutto]

Thanks for this!