Now with more colours and buttons!

This release makes the loader's output red, so that it's easier to visually differentiate from the output of the loaded firmware.

It also makes button 0 on the A7 discard UART input. This is useful if you start loading the wrong thing: the loader will try to process it and will periodically jump into some nonsense code if it receives something that looks like a valid hex file. Holding button 0 will ignore the UART input until you release the button, at which point you can try loading again.

Initial release

Initial release of the UART bootloader.

This has few features, but basically works.