Fix #2

Javascript-files were added once every time a
code-editor was encountered in a page and so
multiple copies of the same Javascript were
loaded in some pages. This should fix this issue.
Fix `--push-gh-pages` flag for create_docs.py
Don't use sphinx module in create_docs.py

The call to `sphinx-build` through the Python `sphinx` module was
causing trouble, as it was reusing sphinx extensions for every
branch. It has now been replaced with a call to `sphinx-build` through
the command line instead.