Add uView.screenBuffer() for access to screen RAM.

Returns a pointer to the start of the RAM screen buffer for direct write and read access.

Users can still mix all the regular display drawing and manipulation functions along side of using direct buffer access. For instance, you could use uView.clear(), uView.setCursor() and uView.print() to put some text somewhere on the screen. Then you could use direct screen buffer access to draw in other areas, before using uView.display() to show it all.