Usage of Glesv3

On file texturator.c, there is some include to "GLES3/gl3.h" and "GLES3/gl3ext.h" but the configure and meson limit the dependency to glesv2.

Does the usage of glesv3 functionality can be put under specific flag ? (Not all embedded platform support glesv3 for the moment).

See on master branch SHA1: be24eade