Merge branch 'ps/history-split'

"git history" learned the "split" subcommand. * ps/history-split: builtin/history: implement "split" subcommand builtin/history: split out extended function to create commits cache-tree: allow writing in-memory index as tree add-patch: allow disabling editing of hunks add-patch: add support for in-memory index patching add-patch: remove dependency on "add-interactive" subsystem add-patch: split out `struct interactive_options` add-patch: split out header from "add-interactive.h"