see if i can integrate µnit into C implementation

[crockeo]

https://nemequ.github.io/munit/#getting-started

i want to use this for some of the more complicated stuff (like write_descriptors) to make sure that everything works as expected

might be something good to do with https://github.com/buserror/simavr? i wonder if i can run AVR on this and then bail when assertions fail...

[crockeo]

another part of this is splitting the app into two main chunks:

• AVR-specific things, which will constitute the "application"
• platform-independent things, which will be the "library"

the library can be µnit tested while the application can't