Avoid the use of DOM to fix problems with CocoonJS

There are some accelerated canvas engines which haven't full DOM
support and always have the canvas at full screen. Some of them
(at least CocoonJS) have problems with the code used to calculate
the offset logic, so a "force full screen" mode is needed to make them
work.
Merge pull request #68 from andresviedma/master

Avoid the use of DOM to fix problems with CocoonJS