stmhal: USB CDC and MSC device work together.
Merge branch 'master' of github.com:micropython/micropython
stmhal: Tidy up USB device configuration.  Make it use less RAM.
sthmal: Remove obsolete files.
stmhal: Tidy up USB CDC+MSC device some more.
stmhal: Add PYBv10 config; add RNG support.
stmhal: Add os module with a few basic functions.
stmhal: Add time module with sleep function.
stmhal: Add servo driver.
objgenerator: Keep exception stack within generator object, like value stack.

This is required to properly handle exceptions across yields.
objgenerator: Implement throwing exceptions out of generator.
objgenerator: Implement .throw() method to throw exceptions into generator.