Add pewpew_m4; Improve snekboard; don't use NeoPixels when clock is wrong
Note: if you already have v3.9.0, there is no strong reason to upgrade to this release unless you're seeing spurious NeoPixel lighting when starting the user program.
- Add PewPew M4 board. Thanks @deshipu.
- Use both NeoPixels on snekboard. Thanks @keith-packard.
- Don't attempt to use NeoPixels when clock speed won't allow it. Thanks @keith-packard.