menu: support <separator />

Add theme options:
- menu.separator.width
- menu.separator.padding.width
- menu.separator.padding.height
- menu.separator.color

Support separator lines defined by <separator />

Note that separator labels (with text) defined by <separator label="" />
are not supported.

docs/labwc-theme.5.scd

@@ -101,6 +101,18 @@ elements are not listed here, but are supported.
 *menu.items.active.text.color*
 	Text color of active menu item
 
+*menu.separator.width*
+	Line thickness of menu separators. Default 1.
+
+*menu.separator.padding.width*
+	Space on the left and right side of each separator line. Default 6.
+
+*menu.separator.padding.height*
+	Space above and below each separator line. Default 3.
+
+*menu.separator.color*
+	Menu separator color. Default #888888.
+
 *osd.bg.color*
 	Background color of on-screen-display
 

docs/themerc

@@ -31,10 +31,13 @@ menu.items.bg.color: #fcfbfa
 menu.items.text.color: #000000
 menu.items.active.bg.color: #dddad6
 menu.items.active.text.color: #000000
+menu.separator.width: 1
+menu.separator.padding.width: 6
+menu.separator.padding.height: 3
+menu.separator.color: #888888
 
 # on screen display (window-cycle dialog)
 osd.bg.color: #dddda6
 osd.border.color: #000000
 osd.border.width: 1
 osd.label.text.color: #000000
-