Changes

: Fix transparency in <TT>copy()</TT> function. Ticket @[https://processing-js.lighthouseapp.com/projects/41284/tickets/1055-copy-doesnt-handle-transparency-properly lighthouse]

: When using copy() on an image with transparency, the transparency overwrites the background color. See the screenshots to compare against p5. The image is a red splatter with transparent background and the background is green.

* Documentation