`theme/gitline` appears to have copied an older(?) version of `powerline/powerline.base`. I'd like to eliminate the duplicate, so this is the first step.
- Add functions from `powerline/powerline.base` to `gitline/powerline.base`. These functions are NOT hooked up yet.
- Bring `__powerline_left_segment()` and `__powerline_prompt_command()` closer together.
- handle unbound parameters
- fix `$POWERLINE_COMPACT` behavior to consistently match documentation
- local some variables
[Toolbox](https://github.com/containers/toolbox) is an containerized
development environment. This commit adds a promot to powerline when it
is running inside a toolbox.
John D Pell
Kan Li
Ira Abramov
Zanark