added zip()
sorted
Cleaned up sorted() as per Damien's suggestions.
Made sorted() raise an exception instead of aborting when given no arguments; moved around some things in objfun.c as a consequence
Merge remote-tracking branch 'upstream/master' into builtins

Conflicts:
	py/builtin.c
	py/builtin.h
	py/runtime.c
Merge pull request #165 from chipaca/builtins

added zip()