ILI9340 partial emulation; writes to PNG on shutdown.

* Ignores all commands except cmdRamWrite.
* Translates 16-bit pixels to 24-bit RGBA image data.
* Ignores correct address windows etc.
* Writes to ili9340.png on shutdown.

Good enough to see some rough color data being written once to video
RAM, but does not handle redraws etc yet.
options.go comments and blank lines removed.
CLI option -ili9340 attaches ILI9340 TFT display to 6522 port B.