Revert "I now realize that removing unigrams as if they had been parsed into bigrams is impossible, because we need to know term order to know if any given unigram was covered by 1 or 2 bigrams. This is the end of the line for this little experiment."

This reverts commit 87d2922e1cab9927f71553ed7aaf5d958d904cbe.
Revert "Remove unigram components of bigrams from document vectors"

This reverts commit 9505d4c24703781c613639595114bc05b54df694.
Generate bigrams, but don't try to remove the component unigrams for retained bigrams form the document vector.