Remove the big endless loop from pycardium main and instead use
epic_exec("") to switch to REPL.  This way, any MicroPython state is
reset and also all hardware will be in a clean reinitialized state.

This also means that pycard10.py will now run scripts in a clean
environment that is not tainted by whatever was running before.

Fixes #212.

Signed-off-by: Rahix <rahix@rahix.de>