doc: stash: split options from description (2)

doc: stash: split options from description (2)

Together with the previous patch, this brings docs for `git stash` to
the common layout used for most other commands (see for example docs
for `git add`, `git commit`, `git checkout`, `git reset`) where all
options are documented in a separate list.

After some thinking and having a look at docs for `git svn` and
`git `submodule`, I have arrived at following conclusions:
  * Options should be described in a list rather then text to
    facilitate lookup for user.
  * Single list is better then multiple lists because it avoids
    copy&pasting descriptions between subcommands (or, without
    copy&pasting, user will have to look up missing options in other
    subcommands).
  * As a consequence, commands section should only give brief info and
    list possible options. Since options have good enough names, user
	will only need to look up the "interesting" options.
  * Every option should list which subcommands support it.

I have decided to use alphabetical sorting in the list of options to
facilitate lookup for user.

There is some text editing done to make old descriptions better fit
into the list-style format.

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>