Inspired by Linux's Bloat-O-Meter, code_size.py wraps nm to provide
function-level code size, and supports detailed comparison between
different builds.
One difference is that code_size.py invokes littlefs's build system
similarly to test.py, creating a duplicate build in the "sizes"
directory. This makes it easy to monitor a cross-compiled build size
while simultaneously testing on the host machine.
