DOC/CLN: remove temporaries
CLN/BUG: tag locals with their creating instance id
DOC: add a more detailed DataFrame.eval docstring
DOC: add simple examples to query/eval
DOC/CLN: move R example to r comp docs
DOC: clean up R comparision docs
CLN: remove extra print expr.py
TST: ensure random column name is a valid identifier
BUG: maybe expression should check for in/not in
DOC: explain why filtering is needed for certain expressions