Script for window snapping

Based on ideas in a script found at http://icculus.org/pipermail/openbox/2013-January/007772.html

Written by damo damo@bunsenlabs.org October 2015

The script snaps a window to left or right halves of screen, or top and bottom, using X window properties for getting and storing values. Left, right, top, or bottom screen margins can be specified (negative values allowed); Works with dual monitors - windows will snap to edges of monitor they are on; Honours user-defined Openbox left and right screen margins; Works with decorated and undecorated windows, and windows with no borders; Doesn't cover panels at top,bottom, desktop left or desktop right.

REQUIRES: xdotool, wmctrl

TODO: Account for _NET_WORKAREA with top/bottom snapping if panel only appears on the other monitor.