python: use tee when joining on single sequence
python: by uses rowfunc, not tee
data: CSV schema detection robust to homogenous data
expr: Collect operation
expr: collect depends on new common_ancestor function
expr: RowWise superclass
ensure multi-level rowfuncs work well
python: Collect and associated utility functions
spark: collect - just a test, handled by python rowfunc
pandas: collect
ancestors punts on non RowWises
sql: Collect
expr: new test and two bugfixes

1.  __truediv__ = __div__
2.  Label.schema used to have an extra list packing
rename spark tests test_spark to avoid testing
rename Collect to Merge
Merge pull request #328 from mrocklin/jaccard-fix

Jaccard fix
data: small fixes to csv mode
docs: update data descriptor.rst
docs: revamp index
update dependencies