man `git bisect` helpers

for viewing the earliest-known bad commit, number of commits currently
from earliest-known bad commit / latest-known good commit
add `git hash` helper to print short SHA hash

includes aliases: hashes, sha, shas
helper for moving files+history to a new git repo

`git-recreate-file` a.k.a. `git rf`
`git rf` preserves initial commit permissions
record a bunch of TODOs in `git rf`