Merge pull request #17 from tkruse/repchangelog

Diverse changes after discussion in Buildsystem sig.
update REP 3 for hydro and updated rules for target platforms
Merge pull request #26 from dirk-thomas/master

update REP 3 for hydro and updated rules for target platforms
missing newline
phrasing
more explicit on the topic of mixing changlog and other content in the same file (README.rst)