Added an argument to output to any filelike object.

Defaults to sys.stdout. My editor added a newline to the end of the
file, which is PEP8 compliant, so I left it in.
Added documentation for the output_to argument.
Merge branch 'output_to_arbitrary' of https://github.com/Auv5/tqdm into Auv5-output_to_arbitrary

Conflicts:
	tqdm.py
Change the output_to argument to 'file', like in print().
Change the default to stderr, since I actually think it's more 'correct'.