Merge pull request #3 from eerolinna/patch-1

Small formatting fix in README.md

remove-stopwords now works with lists of word token frequency pairs

cosine-similarity added to ToC

cosine-similarity. Tweaks to dtm/tdm

dtm function and docs added

tdm now accepts rest arg instead of a list

Added corpus parameter description

Documentation for tdm added

term-document-matrix tdm now returns a proper tf-idf matrix

term-document-matrix initial commit. unfinished.

Initial work on tf-idf matrix

document->tokens moved to text processing

Covariance procedure added

n-gram extraction added