Only calcsize() and unpack() functions provided so far, for little-endian
byte order. Format strings don't support repition spec (like "2b3i").

Unfortunately, dealing with all the various binary type sizes and alignments
will lead to quite a bloated "binary" helper functions  - if optimizing for
speed. Need to think if using dynamic parametrized algos makes more sense.

That's how CPython has it, in particular, "import __main__" should work.

So far just includes "open" function, which should be supplied by a port.

TODO: Make the module #ifdef'ed.

Comes with some refactoring of code and renaming of files.  All modules
are now named mod*.[ch].

mp_module_obj_t can now be put in ROM.

Configuration of float type is now similar to longint: can now choose
none, float or double as the implementation.

math module has basic math functions.  For STM port, these are not yet
implemented (they are just stub functions).

Only works on modules and class instances.

Currently, MicroPython strings are mix between CPython byte and unicode
strings. So, conversion is null so far. This dummy implementation is
intended for compatibility with CPython (so, same code can run on both).

These are micropython.mem_total(), .mem_current(), .mem_peak(). These are 3
individual functions with simple scalar return value to make sure that
calls to these functions themselves have minimal (hopefully zero) impact on
memory allocation.

A big change.  Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object).  This scheme follows CPython.  Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.

Also change name prefix, from py_ to mp_ (mp for Micro Python).