[bobthefish] Use `hg root` instead of `hg stat` for in_hg
[bobthefish] Don't break when hg/git not found
[bobthefish] Add ☿ (mercury) glyph to hg prompt

This makes it easier (possible?) to distinguish between hg and git repos at a glance.
[bobthefish] Switch git/hg priority in prompt

Add TODO to do this right :P
Revert "Gitignore changes"

This reverts commit 8b94f572f170510f8fb0e2f51a657e267dc86241.
[bobthefish] DRY: we don't need two pwd-relative-to-project funcs
[bobthefish] More consistent project dir func names