Changes

Made timed garbage collections only happen if window is shown. Various
changes to reduce garbage creation: Switched from GUILayout to GUI
Replaced buttons with Ctrl-NumPadPlus and Ctrl-NumPadMinus hotkeys Only
update rate string when necessary to avoid a boxing, a ToString call and
a string.Format all of which allocate an object Build rate string by
careful use of a StringBuilder so only the final string is allocated
 (commit: 76b2325)

Added Ctrl-NumPadDivide to toggle timed collection independently of the
window state
 (commit: 3848acc)