This release is mostly internal improvements/fixes.
Notable user-facing changes are:
- The pull subcommand learned the ability to pull with a note, for
example `gbp pull --note "Built with --emptytree" babette 999`
- Unknown theme names are no longer disregarded. This is to allow for
third-party subcommands, (e.g. `gbp-ps`) to have their own theme
names.