docs: python bindings howto
* Complete typographic overhaul. * Removed all section level indentation since it does not affect output formatting, but might affect source code examples. * In text-mode stripped out all tabs which had crept in and replaced them with four spaces. * Updated all code examples (again) to conform with Python-mode. * Bumped version number in preparation for next release of GPG 2.2.9 and corresponding GPGME release.