A GLES2-specific tweak is now documented for the GUI in 3D demo.
This also tweaks shadow quality and performance to find a better
balance and result in smoother shadows, including when using GLES2
(thanks to the use of PCF13 shadow filter mode).
In demos that allow falling back to GLES2, ETC1 texture import
is enabled to allow exporting to Android or HTML5 without having
to tweak anything.
