ENH: add new computation module and toplevel eval function
ENH/TST: add new instance testing functions and their tests
BUG: prevent certain index types from joining with DatetimeIndex
TST/ENH: add 2d bare numpy array and nan support
ENH: add modulus support
TST: add failing modulus tests
CLN: use format string for unicode
CLN: remove engine detection and manip for datetimes
ENH: add Term and Constant
CLN: clean up expressions.py
CLN: move Scope to expr.py
TST: add failing isexpr test
CLN/ENH: add new interface to encapsulate Terms and Constants
ENH: allow an already-parsed expression to be passed to eval