Until recently (or maybe not too recently) ES3 extension header was
"currently empty", now the extension header is shared with ES2. It's
nice to finally get rid of all the weird ifndefs.
Renamed AbstractTexture::maxSupportedLayerCount() to maxLayers(),
which is in fact alias to Shader::maxCombinedTextureImageUnits(). Also
renamed Samples::maxSupportedAnisotropy() to maxAnisotropy(). It now
has slightly confusing naming, will fix that later. Both
original functions are now alias to new ones to retain source
compatibility, will be removed in future releases.
Also printing the values in magnum-info.
Solves another trivial choice (similar to the one with TextureFormat
etc. in 7de45c98b1), less typing and also
preparation for ARB_sampler_objects extension.