Use hooks to speed up prompt

[michaeldfallen]

The radar's local and remote commits can be slow, on heavy repos it can be very slow. We could use git hooks to only calculate the local and remote commits each time push, fetch, pull, commit etc events occur.

The precalculated strings could then be read from files in the .git folder quite quickly on each render.

[nicolaiskogheim]

Yes, please! I want this.

[michaeldfallen]

I've run some performance tests and it seems to be the git status --porcelain call (in my slowest repo the full prompt renders in 0.25s and git status takes 0.245s. I'm going to try firing an async git status and read that off disk. Perhaps that will speed things up.

[michaeldfallen]

Anyone interested in this feature, I have pushed a working prototype of running the different indicators asynchronously and refreshing the prompt when ready in #83. It's another approach to solving the need this is born out of and worth a look.