Takes raw text rdd and transforms it into rdd containing sentences only

Takes sentences only rdd and transforms it into rdd of key-value pairs,
the key being the sentence, and the value being list of tokens

Takes sentences only rdd and transforms it into gin index rdd,
the key is a word and the value is an iterable of sentences

Takes gin rdd and returns rdd of sentences that contain the token

Takes sentence-token list rdd and transforms it into the vocabulary rdd
containing only the alphabetical tokens from the text

Build tf breakdown of sentence-token list. 
The resulting key is sentence-token pair.

Build idf breakdown of sentence-token list.
The resulting key is sentence.

Build tf-idf breakdown of sentence-token list.
The resulting key is sentence-token.