Rationale: setting up the stack (state for locals and exceptions) is
really part of the "code", it's the prelude of the function.  For
example, native code adjusts the stack pointer on entry to the function.
Native code doesn't need to know n_state for any other reason.  So
putting the state size in the bytecode prelude is sensible.

It reduced ROM usage on STM by about 30 bytes :)  And makes it easier to
pass information about the bytecode between functions.

py: Support closures with default args.

Originally, .methods was used for methods in a ROM class, and
locals_dict for methods in a user-created class.  That distinction is
unnecessary, and we can use locals_dict for ROM classes now that we have
ROMable maps.

This removes an entry in the bloated mp_obj_type_t struct, saving a word
for each ROM object and each RAM object.  ROM objects that have a
methods table (now a locals_dict) need an extra word in total (removed
the methods pointer (1 word), no longer need the sentinel (2 words), but
now need an mp_obj_dict_t wrapper (4 words)).  But RAM objects save a
word because they never used the methods entry.

Overall the ROM usage is down by a few hundred bytes, and RAM usage is
down 1 word per user-defined type/class.

There is less code (no need to check 2 tables), and now consistent with
the way ROM modules have their tables initialised.

Efficiency is very close to equivaluent.

Addresses issue #377.

Just to keep things consistent :)

vm: Implement raise statement w/o args (reraising last exception).

This gets "value" of exceptions in the sense as it's defined for
StopIteration.value (i.e. args[0] or None).

TODO: This really should be inline function.

Return with value gets converted to StopIteration(value). Implementation
keeps optimizing against creating of possibly unneeded exception objects,
so there're considerable refactoring to implement these features.

py/objstr.c: Implement str.rfind() and add tests for it, refactor find_subbytes().

They still exist in commented-out form in objexcept.c if they are ever
needed.

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

Add mp_obj_module_register

Some changes that I forgot to push with my last pull request

Fix adc to work with resolution changes.

* Add function to load static modules.
* Use module_register to pyb module.

Added support for the ADC channels and mappings to make_pins.py

I'm not sure if the hal properly deals with the channel 16/18 differences
between the 40x and 42x. It seems to deal with it partially. This particular
aspect will need testing on a 42x or 43x.