optimized ngrams versions of levenshtein and subs-only searches
making tox.ini compatible with Travis-CI
dropped support for Python3.1 due to problems with unittest2py3k test discovery
Merge branch 'master' into kevin
upgraded benchmarking code
changed input type validation to an assertion in common.search_exact()
added common.count_different_items_with_max(seq1, seq2, max_different)
several optimizations in _find_near_matches_substitutions_ngrams()