Get most basics working

- Control (at least) 1 neopixel
- Add basic blinky panic handler
- Support N-key rollover
- Test GPIO pins

src/neopixel2.pio

@@ -0,0 +1,8 @@
+.program ws2812
+.origin 0
+.wrap_target
+   out x 1
+   set pins,1 [1]
+   mov pins,x [1]
+   set pins,0
+.wrap