Extend parametertreeparser; fixes #54 (first proposal)

The parametertree parser can now handle

[prefix] # comment key = value

This is one way of fixing #54 (closed). !247 (closed) would be another. Please see #54 (closed) for a discussion.

mentioned in merge request !247 (closed)

mentioned in issue #54 (closed)

OK as a quick fix, I guess, but the configparser really needs to error out on stuff that it does not understand in the long run.

merged

mentioned in commit 97229ab6