test for ambiguities
add doctests around various utility functions
csv: add missing values to None test
into: numpy and python Nones
minor docstrings in csv
sparksql: only define functions if pyspark is defined
Merge branch 'test-ambiguities' into chunked-csv
remove unicodecsv requirement
xfail nan/none tests
Merge pull request #3 from mrocklin/chunked-csv

Chunked csv