python bindings: core — PEP8 compliance
python bindings: core — PEP8 compliance

* Fixed most of the PEP8 errors in core.py
* Those remaining may need more than little edits and are a bit
  strange (too clearly the result of a programmer who has spent far
  too much time dealing with Lisp so that for Python it looks
  ... strange).

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme