patch 8.1.2019: 'cursorline' always highlights the whole line

Problem:    'cursorline' always highlights the whole line.
Solution:   Add 'cursorlineopt' to specify what is highlighted.
            (closes #4693)
diff --git a/runtime/doc/quickref.txt b/runtime/doc/quickref.txt
index 90e76f2..bfc387e 100644
--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -670,6 +670,7 @@
 'cursorbind'	  'crb'     move cursor in window as it moves in other windows
 'cursorcolumn'	  'cuc'	    highlight the screen column of the cursor
 'cursorline'	  'cul'	    highlight the screen line of the cursor
+'cursorlineopt'	  'culopt'  settings for 'cursorline'
 'debug'			    set to "msg" to see all error messages
 'define'	  'def'     pattern to be used to find a macro definition
 'delcombine'	  'deco'    delete combining characters on their own