Add gitsummary

[glenreesor]

New App Submission

• [x] I've read the contribution guidelines.

Repo or homepage link: https://github.com/glenreesor/gitsummary

Description: A single command to provide the following info about the current git repo, all nicely formatted with color:

• stashes
• file statuses
• branch list
  • number of commits ahead/behind remote tracking branch
  • number of commits ahead/behind merge target

Also includes two helpers:

• gmon
  • repeatedly clear the screen and run gitsummary with a 1s delay -- keep this in a terminal to provide current status of your repo
• gitsummaryShellHelper
  • provide a concise summary of your repo, suitable for use in a shell prompt

Why you think it's awesome: Stashes, file statuses, branch lists, and the branch ahead/behind info provide a great summary of the state of a repo. This command does it all at once and in a nice format.

Full test suite that passes on Linux, MacOS, and Windows.