`prompt.showinfo` for enabling or disabling it globally or per
repository. It can be globally disabled by not loading the `git-info`
module at all, and prompts currently will not break (and in the future
should still not break) if the module is not loaded.
This removes one git call that is used to check for the
`prompt.showinfo` configuration value.
that, when defined, will be set if branch is both ahead and behind of
remote. If not defined, the `ahead` and `behind` contexts will still be
set, as how they worked previously.
based on the Prezto git module
[function](https://github.com/sorin-ionescu/prezto/blob/master/modules/git/functions/git-info)
and further refactored and simplified.
What changed:
- Commit format only in 'detached HEAD' state, so
`$(coalesce "%b" "%c")` is not needed, because you only get one of
those.
- Removed the `added`, `deleted`, `modified`, `renamed` and `unmerged`
verbose contexts.
- `git status` is only used in verbose mode.
- In non-verbose mode, the `untracked` context is not available, and
also untracked files are not considered for computing the `dirty`
context. Using `git status` or checking for untracked files is
[expensive](https://gist.github.com/sindresorhus/3898739).
