This is like notmuch-search-filter-by-tag, but creates a new search
rather than filtering the current search. We add this to
notmuch-common-keymap since this can be used by many contexts. We bind
to the key "t", which is the same key used by
notmuch-search-filter-by-tag in notmuch-search-mode-map. This is done
intentionally since the keybinding for notmuch-search-mode-map can be
seen as a specialization of creating a new search.
This change was motivated for use in "notmuch-hello". It is a more
convenient way to search a tag than expanding the list of all tags. I
also noticed many saved searches people use are simply tags.
This adds a file under devel listing all the keybindings sorted by key
in the main three modes (search, show and tree).
To reduce clutter it only lists the single key "unmodified"
keybindings: I think all our uses of prefixes and modifiers are
natural variants of the unmodified binding (eg M-n compared to n in
show mode)
This should make easier to see what keybindings are available when
adding new features.
