anchor: love.graphics.captureScreenshot
  Creates a screenshot once the current frame is done (after love.draw has finished).
  
  Since this function enqueues a screenshot capture rather than executing it immediately, it can be called from an input callback or love.update and it will still capture all of what's drawn to the screen in that frame.
  love.graphics.captureScreenshot( filename )
  filename string The filename to save the screenshot to. The encoded image type is determined based on the extension of the filename, and must be one of the ImageFormats.
  love.graphics.captureScreenshot( callback )
  callback function Function which gets called once the screenshot has been captured. An ImageData is passed into the function as its only argument.
  love.graphics.captureScreenshot( channel )
  channel Channel The Channel to push the generated ImageData to.