bumpversion: allow for development releases
bumpversion: allow for development releases

- unreleased versions (in version control) have the .dev suffix
- optional released development releases have a .devN suffix (PEP 440)
- don't place the release date in the change log (doesn't make sense for
  .dev versions)

brechtm/rinohtype,brechtm/rinohtype,brechtm/rinohtype