Implement __aeabi_f2d and __aeabi_d2f

objint_mpz: Quick&dirty implementation of bitwise operations.

Made solely to unbreak int-long.py test which in turn uncovered thinko
with implementation of inplace ops. On mpz level, bitwise ops implemented
only for same-sign numbers, and are not efficient (unconditional calling of
mpn_cmp() is apparently superfluous).

This was a long-standing regression from converting script from sh to python.

As part of this, rejig the way TIM3 is initialised, since it's now
shared by USB CDC and the blue LED PWM.

Fixed some math functions and added more exceptions.

Fixed some math functions and added more exceptions.

objgenerator: Implement exception handling for generators

Fixed modulo operator on ints and mp ints to agree with python. Added intdivmod.c and tests/basics/modulo.py.

This is required to properly handle exceptions across yields.

Added exception hierarchy except for OSError and UnicodeError (requires arguments). Comment out the errors that aren't needed if memory becomes an issue.