patch 8.0.1206: no autocmd for entering or leaving the command line

Problem:    No autocmd for entering or leaving the command line.
Solution:   Add CmdlineEnter and CmdlineLeave.
diff --git a/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index b4b064c..da35c27 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -492,6 +492,18 @@
 				command is defined.  An alternative is to
 				always define the user command and have it
 				invoke an autoloaded function.  See |autoload|.
+							*CmdlineEnter*
+CmdlineEnter			After moving the cursor to the command line,
+				where the user can type a command or search
+				string.
+				<afile> is set to a single character,
+				indicating the type of command-line.
+				|cmdwin-char|
+							*CmdlineLeave*
+CmdlineLeave			Before leaving the command line.
+				<afile> is set to a single character,
+				indicating the type of command-line.
+				|cmdwin-char|
 							*CmdwinEnter*
 CmdwinEnter			After entering the command-line window.
 				Useful for setting options specifically for