Add `Branch#get_properties`
Use `Branch#get_properties` in `#get_property`
Speed up `#branch_list_line` by 3–4x!
`#all_properties` -> `#all_property_names`
Reduce test repetition
Rename RESERVED_BRANCH_{PROPERTIES,PROPERTY_NAMES}
Note branch listing speedup in history
Support `twig init-completion --force`

Allows overwriting any existing completion script.
Clarify `twig init-completion --force` success msg
Fix `\n` in generated `twig-completion.bash`
Add `twig init-completion --force` to history
Add `twig init-completion --force` to readme
Add Twig URL to each subcommand
Suggest `init-completion --force` if script exists
Add `bin/twig-diff`
twig-diff: Abort if no diff branch
Add completion for `twig diff <branch>`
twig-diff: Support passing options to `git-diff`
twig-diff: Document usage
twig-diff: Expand usage docs