treat particle as sprite;
support particle group;
add child_visible interface

Signed-off-by: rainfiel <rainfiel@ejoy.com>
Merge branch 'master' of ssh://oa.ejoy.com/ejoy2d
new particle example res

Signed-off-by: rainfiel <rainfiel@ejoy.com>
update particle example ex03.lua
bugfix: matrix.new() return identity matrix
Merge branch 'master' of ssh://oa.ejoy.com/ejoy2d