docs: clean up `--empty` formatting in git-rebase(1) and git-am(1)

Both of these pages document very similar `--empty` options, but with
different styles. The exact behavior of these `--empty` options differs
somewhat, but consistent styling in the docs is still beneficial. This
commit aims to make them more consistent.

Break the possible values for `--empty` into separate sections for
readability. Alphabetical order is chosen for consistency.

In a future commit, we'll be documenting a new `--empty` option for
git-cherry-pick(1), making the consistency even more relevant.

Signed-off-by: Brian Lyles <brianmlyles@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-am.txt

@@ -66,13 +66,19 @@ OPTIONS
 --quoted-cr=<action>::
 	This flag will be passed down to 'git mailinfo' (see linkgit:git-mailinfo[1]).
 
---empty=(stop|drop|keep)::
+--empty=(drop|keep|stop)::
-	By default, or when the option is set to 'stop', the command
+	How to handle an e-mail message lacking a patch:
-	errors out on an input e-mail message lacking a patch
++
-	and stops in the middle of the current am session. When this
+--
-	option is set to 'drop', skip such an e-mail message instead.
+`drop`;;
-	When this option is set to 'keep', create an empty commit,
+	The e-mail message will be skipped.
-	recording the contents of the e-mail message as its log.
+`keep`;;
+	An empty commit will be created, with the contents of the e-mail
+	message as its log.
+`stop`;;
+	The command will fail, stopping in the middle of the current `am`
+	session. This is the default behavior.
+--
 
 -m::
 --message-id::

Documentation/git-rebase.txt

@@ -289,17 +289,24 @@ See also INCOMPATIBLE OPTIONS below.
 +
 See also INCOMPATIBLE OPTIONS below.
 
---empty=(drop|keep|ask)::
+--empty=(ask|drop|keep)::
 	How to handle commits that are not empty to start and are not
 	clean cherry-picks of any upstream commit, but which become
 	empty after rebasing (because they contain a subset of already
-	upstream changes).  With drop (the default), commits that
+	upstream changes):
-	become empty are dropped.  With keep, such commits are kept.
++
-	With ask, the rebase will halt when an empty commit is applied
+--
-	allowing you to choose whether to drop it, edit files more, or just
+`ask`;;
-	commit the empty changes.
+	The rebase will halt when the commit is applied, allowing you to
-	When the `-i`/`--interactive` option is used, the default becomes ask.
+	choose whether to drop it, edit files more, or just commit the empty
-	Otherwise, when the `--exec` option is used, the default becomes keep.
+	changes. This option is implied when `-i`/`--interactive` is
+	specified.
+`drop`;;
+	The commit will be dropped. This is the default behavior.
+`keep`;;
+	The commit will be kept. This option is implied when `--exec` is
+	specified unless `-i`/`--interactive` is also specified.
+--
 +
 Note that commits which start empty are kept (unless `--no-keep-empty`
 is specified), and commits which are clean cherry-picks (as determined
@@ -704,7 +711,7 @@ be dropped automatically with `--no-keep-empty`).
 Similar to the apply backend, by default the merge backend drops
 commits that become empty unless `-i`/`--interactive` is specified (in
 which case it stops and asks the user what to do).  The merge backend
-also has an `--empty=(drop|keep|ask)` option for changing the behavior
+also has an `--empty=(ask|drop|keep)` option for changing the behavior
 of handling commits that become empty.
 
 Directory rename detection