Fix (some) whitespace according to PEP-8.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
Remove unused imports.
Follow PEP-8 and make imports in separate lines (and sorted).
Make script follow PEP-8 more rigidly with PythonTidy.
README.md: Fix edx domain.

The site `edx.com` is a very different one from `edx.org` (which is the one
we are interested in).
README.md: Reword, fix spelling, punctuation and markup.
Make python files executable.
Merge pull request #8 from rbrito/fixes

General fixes