Document latest guidelines / convert them from .json to .rst
so that they can be included in the documentation.
The patch converts all guidelines since 2018 when this convert
happend for the last time.
The patch also enables pep8 job on doc changes as there is a .rst
check implemented within tox' pep8 env.
Change-Id: I8a65dfb15c5572bedf1bbf36bfa2143df47010bb