add n_kmers() to CountingHash
n_kmers -> n_unique_kmers
Merge pull request #652 from ged-lab/fix/n_kmers

add n_kmers() to CountingHash
Added screed and read_parser stream testing. Currently marked as known_failing since they fail with existing systems. non-gzip streaming works in screed 0.7.1
Reverted inadvertent change to tests/test_graphs.py
Cleaned up formatting in streaming tests.
Renamed streaming test helper functions to something more explicit.
Cleaned up fifo/blk testing logic structure to be cleaner
Added docstrings to helper functions to better explain functionality
Cleaned up some comments
Updated docstring formatting
Cleared up logical structure
updated docstring to be clearer.
Reducing import bloat
updated comments
removed extraneous known_failing attr