STM32L4-based motor controller

I built some motor controller hardware, and I wanted to use an open-source toolchain to make it go.

Build and debug prerequisites

• scons
• gcc-arm-none-eabi
• gdb-arm-none-eabi
• stlink

Shoutouts

• xpcc, which taught me a great deal about SCons in an embedded context.
• Seth LaForge, from whom I liberally stole compiler flags.