ENH: add toplevel eval function

This also adds a new directory in the top level pandas directory, called
"computation". Further development on out-of-core processing should be placed
in this directory.
ENH: add string testing capability to core.common
TST/ENH: add nanequal

This function allows one to compare two arrays for equality, while treating
nans as equal, optionally it allows the use of numexpr for evaluation possibly
speeding up comparison
ENH: add randbool testing function to create random boolean arrays
ENH: beef up the alignment algo
CLN/ENH: use values because we cannot depend on the array interface
CLN/ENH: give ops a better repr
ENH: clean up indexing and deal with series axis stuff
ENH: add type testing functions and test stubs for them
TST/ENH: add wacky alignment tests
CLN: remove unused junk
TST/CLN: get rid of generated tests