Garbage collection on demand touching "stats"

If stats are shown it's possible to enable a 'force garbage collector'
call on touch. Usefull for debug purposes
MultiplyColor logic

Removed old and wrong multiplyAlpha logic, replaced by MultiplyColor
that allows to reflect the displayList color status even on Quad and
objects draws using pixel shader
Added PerformanceTimer

performance timer is based on socket.gettime. It returns millisec
elapsed since initialization of a timer or the millisec elapsed since
last getDeltaTime call.
Updated documentation

ldoc comments / documentation updated to latest revision