Get rid of the messy `bump*.sh` scripts variants with a single one with
positional arguments (all optional):
- -v: the new version number (default: current)
- -b: the new build number (default: current + 1)
- -s: the initial build for the CHANGELOG diff (default: latest tag)
- -na: do not update the API (default: do update it)
- -nl: do not update the CHANGELOG (default: present editor)
- -d: dry run
Fixes#948
Davide