tests: Add a suite of tests specifically for the pyboard.
In tests/pyb is now a suite of tests that tests the pyb module on the pyboard. They include expected output files because we can't run CPython on the pyboard to compare against. run-tests script has now been updated to allow pyboard tests to be run. Just pass the option --pyboard. This runs all basic, float and pyb tests. Note that float/math-fun.py currently fails because not all math functions are implemented in stmhal/.