patch 8.0.1782: no simple way to label quickfix entries

Problem:    No simple way to label quickfix entries.
Solution:   Add the "module" item, to be used instead of the file name for
            display purposes. (Martin Szamotulski, closes #1757)
diff --git a/runtime/doc/quickfix.txt b/runtime/doc/quickfix.txt
index de80c68..96085d2 100644
--- a/runtime/doc/quickfix.txt
+++ b/runtime/doc/quickfix.txt
@@ -1220,6 +1220,7 @@
 Basic items
 
 	%f		file name (finds a string)
+	%o		module name (finds a string)
 	%l		line number (finds a number)
 	%c		column number (finds a number representing character
 			column of the error, (1 <tab> == 1 character column))
@@ -1264,6 +1265,11 @@
 output.  Like the output of the "grep" shell command.
 When the pattern is present the line number will not be used.
 
+The "%o" conversion specifies the module name in quickfix entry.  If present
+it will be used in quickfix error window instead of the filename.  The module
+name is used only for displaying purposes, the file name is used when jumping
+to the file.
+
 Changing directory
 
 The following uppercase conversion characters specify the type of special