patch 9.0.0342: ":wincmd =" equalizes in two directions

Problem:    ":wincmd =" equalizes in two directions.
Solution:   Make ":vertical wincmd =" equalize vertically only and
            ":horizontal wincmd =" equalize horizontally only.
diff --git a/runtime/doc/windows.txt b/runtime/doc/windows.txt
index 13f648f..32ec102 100644
--- a/runtime/doc/windows.txt
+++ b/runtime/doc/windows.txt
@@ -256,9 +256,16 @@
 						*:vert* *:vertical*
 :vert[ical] {cmd}
 		Execute {cmd}.  If it contains a command that splits a window,
-		it will be split vertically.
+		it will be split vertically.  For `vertical wincmd =` windows
+		will be equialized only vertically.
 		Doesn't work for |:execute| and |:normal|.
 
+						*:hor* *:horizontal*
+:hor[izontal] {cmd}
+		Execute {cmd}.  Currently only makes a difference for
+		`horizontal wincmd =`, which will equal windows only
+		horizontally.
+
 :lefta[bove] {cmd}				*:lefta* *:leftabove*
 :abo[veleft] {cmd}				*:abo* *:aboveleft*
 		Execute {cmd}.  If it contains a command that splits a window,
@@ -553,6 +560,10 @@
 		'winheight' and 'winwidth' for the current window.
 		Windows with 'winfixheight' set keep their height and windows
 		with 'winfixwidth' set keep their width.
+		To equalize only vertically (make window equally high) use
+		`vertical wincmd =`
+		To equalize only horizontally (make window equally wide) use
+		`horizontal wincmd =`
 
 :res[ize] -N					*:res* *:resize* *CTRL-W_-*
 CTRL-W -	Decrease current window height by N (default 1).