On OpenGL ES 2.0, create depth renderbuffers in explicit GL_DEPTH_COMPONENT16 format, as GL_DEPTH_COMPONENT is unsupported on some devices. Possibly a fix for #140.
For better performance, avoid backbuffer resolve to texture on OpenGL ES 2.0 and instead prefer to render into a texture if the viewport contents need to be read.
Added note of clip plane being unsupported on OpenGL ES 2.0.