Implemented support for `in` and `not in` operators.
Merge remote-tracking branch 'upstream/master' into containment

Conflicts:
	py/runtime.c
Merge remote-tracking branch 'upstream/master' into containment
Fixed the merge so it worked and compiled and stuff
Merge remote-tracking branch 'upstream/master' into containment
Merge pull request #142 from chipaca/containment

Implemented support for `in` and `not in` operators.