add table object
add columns property
add Projection
add slots and eq and hash
table[...] produces Projection
add relational
add selection
table[Relational] produces Selection
pep8
Relational is a Column
basic pandas computation
add compute layer for python
relational classes hold operator ops
use itertools.itemgetter in place of toolz.get
add compute layer for sqlalchemy
tiny docstrings for table
fix types in sqlalchemy table
add deadbeat doctest to sql, python, pandas compute
add future imports
add arithmetic operations