Widths and x positions no more depend on item->h.

• Adding support for gaps (#3)
• Adding more comments and categorizing function declarations.
• Adding support for EWMH properties (xmenu look is now consistent
  in some window compositors).
• Changing how configuration is done (now all configuration belongs
  to the config structure).

Rather than setting the padding.

I just stole the colors from firefox's context menu.