Create frequency.py

Python script use to compute the term frequency histogram of the livestream data harvested from twitter_stream.py

The frequency of a term is calculated with the following formula:
[# of occurrences of the term in all tweets]/[# of occurrences of all terms in all tweets]

Input:

          $ python frequency.py <tweet_file>


Output

          <term:string> <frequency:float>

For example:

          bar 0.1245