patman: Support multi-line changes in changelogs

This patch adds support to multi-line changes. That is, if one has a line
in a changelog like
- Do a thing but
  it spans multiple lines
Using Series-process-log sort would sort as if those lines were unrelated.
With this patch, any change line starting with whitespace will be
considered part of the change before it.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/README b/tools/patman/README
index a99a68c..52b2cf7 100644
--- a/tools/patman/README
+++ b/tools/patman/README
@@ -270,8 +270,14 @@
 	interpreted by git send-email if you use it.
 
 Series-process-log: sort, uniq
-	This tells patman to sort and/or uniq the change logs. It is
-	assumed that each change log entry is only a single line long.
+	This tells patman to sort and/or uniq the change logs. Changes may be
+	multiple lines long, as long as each subsequent line of a change begins
+	with a whitespace character. For example,
+
+- This change
+  continues onto the next line
+- But this change is separate
+
 	Use 'sort' to sort the entries, and 'uniq' to include only
 	unique entries. If omitted, no change log processing is done.
 	Separate each tag with a comma.