Added check for tmp subdir

http://stackoverflow.com/questions/273192/check-if-a-directory-exists-and-create-it-if-necessary
Made all constants CAPS_AND_UNDERSCORES
Image downloading

For now only downloads JPG. Can probably convert everything with PIL if
I want to, but it's very to see something other than jpg requested.

Also renamed reddit login constants for clarity.
added *_test.py rule for experiments
.gitignore: Ignore all files with _test

Not just .py files
Initial work on Google img search

Doesn't work yet of course, but I wanna move on to other things now. :p