Merge branch 'rr/rebase-stash-store'

Finishing touches for the "git rebase --autostash" feature
introduced earlier.

* rr/rebase-stash-store:
rebase: use 'git stash store' to simplify logic
stash: introduce 'git stash store'
stash: simplify option parser for create
stash doc: document short form -p in synopsis
stash doc: add a warning about using create

diff --cc git-rebase.sh
Simple merge

diff --cc t/t3903-stash.sh
Simple merge