patch 8.2.0861: cannot easily get all the current marks

Problem:    Cannot easily get all the current marks.
Solution:   Add getmarklist(). (Yegappan Lakshmanan, closes #6032)
diff --git a/runtime/doc/usr_41.txt b/runtime/doc/usr_41.txt
index 8fece1a..2642e0b 100644
--- a/runtime/doc/usr_41.txt
+++ b/runtime/doc/usr_41.txt
@@ -724,6 +724,7 @@
 	getcurpos()		get position of the cursor
 	getpos()		get position of cursor, mark, etc.
 	setpos()		set position of cursor, mark, etc.
+	getmarklist()		list of global/local marks
 	byte2line()		get line number at a specific byte count
 	line2byte()		byte count at a specific line
 	diff_filler()		get the number of filler lines above a line