Separator color via config; separator width and on/off via ipc

This patch adds the following features:
1) Configure a color of the separator via config.  It is done like
   bar {
      colors {
         separator #000000
      }
   }
2) A block can have an integer entry "separator_block_width" which
   sets the width of the gap which would follow after the current block.

3) A block can have a boolean entry "separator" and if it is set
   to false, then the drawing of the separating line would be disabled.

docs/i3bar-protocol

@@ -154,6 +154,14 @@ urgent::
 	A boolean which specifies whether the current value is urgent. Examples
 	are battery charge values below 1 percent or no more available disk
 	space (for non-root users). The presentation of urgency is up to i3bar.
+separator::
+	The boolean value false disables drawing of a separating line after the
+	block.  If the field is not present then the separator will be still
+	drawn.  Keep in mind that absence of a separator is only responsible for
+	the line itself, the gap between the items would be still present.
+separator_block_width::
+	The integer value that sets the width of the gap between items in pixels.
+	In the middle of the gap, a separating line is going to be drawn.
 
 If you want to put in your own entries into a block, prefix the key with an
 underscore (_). i3bar will ignore all keys it doesn’t understand, and prefixing

docs/ipc

@@ -507,6 +507,8 @@ background::
 	Background color of the bar.
 statusline::
 	Text color to be used for the statusline.
+separator::
+	Text color to be used for the separator.
 focused_workspace_text/focused_workspace_bg::
 	Text color/background color for a workspace button when the workspace
 	has focus.

docs/userguide

@@ -1155,6 +1155,8 @@ background::
 	Background color of the bar.
 statusline::
 	Text color to be used for the statusline.
+separator::
+	Text color to be used for the separator.
 focused_workspace::
 	Border, background and text color for a workspace button when the workspace
 	has focus.
@@ -1176,6 +1178,7 @@ urgent_workspace::
 colors {
     background <color>
     statusline <color>
+    separator <color>
 
     colorclass <border> <background> <text>
 }
@@ -1187,6 +1190,7 @@ bar {
     colors {
         background #000000
         statusline #ffffff
+        separator #666666
 
         focused_workspace  #4c7899 #285577 #ffffff
         active_workspace   #333333 #5f676a #ffffff