Merge branch 'js/range-diff-wo-dotdot'

There are other ways than ".." for a single token to denote a
"commit range", namely "<rev>^!" and "<rev>^-<n>", but "git
range-diff" did not understand them.

* js/range-diff-wo-dotdot:
  range-diff(docs): explain how to specify commit ranges
  range-diff/format-patch: handle commit ranges other than A..B
  range-diff/format-patch: refactor check for commit range

Documentation/git-range-diff.txt

@@ -28,6 +28,17 @@ Finally, the list of matching commits is shown in the order of the
 second commit range, with unmatched commits being inserted just after
 all of their ancestors have been shown.
 
+There are three ways to specify the commit ranges:
+
+- `<range1> <range2>`: Either commit range can be of the form
+  `<base>..<rev>`, `<rev>^!` or `<rev>^-<n>`. See `SPECIFYING RANGES`
+  in linkgit:gitrevisions[7] for more details.
+
+- `<rev1>...<rev2>`. This is equivalent to
+  `<rev2>..<rev1> <rev1>..<rev2>`.
+
+- `<base> <rev1> <rev2>`: This is equivalent to `<base>..<rev1>
+  <base>..<rev2>`.
 
 OPTIONS
 -------