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.

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.

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

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

Also modify mp_get_index to accept:
1. Indices that are or evaluate to a boolean.
2. Slice indices.
Add tests for these two cases.

If operation will overflow, a multi-precision integer is created.

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).

I.e. as replacement of MP_OBJ_IS_TYPE(), which takes into account subclassing.

Don't need to wrap bitfields in their own struct.  Compiler does the
correct thing without it.

Some functionality is still missing (eg and, or, bit shift), and some
things are buggy (eg subtract).

For this, record argument names along with each bytecode function. The code
still includes extensive debug logging support so far.

Addresses issue #295.

Each built-in exception is now a type, with base type BaseException.
C exceptions are created by passing a pointer to the exception type to
make an instance of.  When raising an exception from the VM, an
instance is created automatically if an exception type is raised (as
opposed to an exception instance).

Exception matching (RT_BINARY_OP_EXCEPTION_MATCH) is now proper.

Handling of parse error changed to match new exceptions.

mp_const_type renamed to mp_type_type for consistency.

Ultimately all static strings should be qstr.  This entry in the type
structure is only used for printing error messages (to tell the type of
the bad argument), and printing objects that don't supply a .print method.

Unlike CPython socket, microsocket object already implements stream protocol
(read/write methods), so makefile() just returns object itself. TODO: this
doesn't take care of arguments CPython's makefile() may accept.

Can't decide which is better for string type, char or byte pointer.
Changing to char removes a few casts.  Really need to do proper unicode.

Structure is back to expected 16 bytes.