* Add `love.graphics.isSupported("hdrcanvas")' to query whether the hardware
actually supports HDR canvases.
* Add optional third argument to `love.graphics.newCanvas(w,h, type)', where
`type' is one of "normal" or "hdr" and defaults to "normal". HDR canvases
use floating point that can have values > 1 to store pixels, allowing for
HDR rendering and other higher level lighting techniques when combined with
pixel effects.
* Add `canvas:getType()'.
Error reporting now resides in Graphics::newCanvas() instead of the
previous location wrap_newFramebuffer(). Changed error text for
"Error in implementation" to point to a possible fix.