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/src/vim.h b/src/vim.h
index 11b7b08..ed12b07 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1295,6 +1295,8 @@
     EVENT_BUFWRITEPOST,		/* after writing a buffer */
     EVENT_BUFWRITEPRE,		/* before writing a buffer */
     EVENT_BUFWRITECMD,		/* write buffer using command */
+    EVENT_CMDLINEENTER,		/* after entering the command line */
+    EVENT_CMDLINELEAVE,		/* before leaving the command line */
     EVENT_CMDWINENTER,		/* after entering the cmdline window */
     EVENT_CMDWINLEAVE,		/* before leaving the cmdline window */
     EVENT_COLORSCHEME,		/* after loading a colorscheme */