reversed function now implemented, and works for tuple, list, str, bytes
and user objects with __len__ and __getitem__.

Renamed mp_builtin_len to mp_obj_len to make it publically available (eg
for reversed).

And not system printf(), like it was before. For this, move pfenv_printf()
from stmhal port to py/.

But much smaller and memory-efficient. Uses Python builtin data structures
(dict, tuple, int) to describe structure layout.

Such mechanism is important to get stable Python functioning, because Python
function calling is handled with C stack. The idea is to sprinkle
STACK_CHECK() calls in places where there can be C recursion.

TODO: Add more STACK_CHECK()'s.

To help with debugging issue like #510 for example.

These are to assist in writing native C functions that take positional
and keyword arguments.  mp_arg_check_num is for just checking the
number of arguments is correct.  mp_arg_parse_all is for parsing
positional and keyword arguments with default values.

Any generated headers go in $(BUILD)/genhdr/, and are #included as
'genhdr/xxx.h'.

Not all functions implemented.  Not enabled on pyboard.

Having an optimized asm implementation is good, but if we want portability,
that's it.

The autogenerated header files have been moved about, and an extra
include dir has been added, which means you can give a custom
BUILD=newbuilddir option to make, and everything "just works"

Also tidied up the way the different Makefiles build their include-
directory flags

Enabled by MICROPY_ENABLE_PROPERTY.

This is alternative implementation of supporting conditionals in qstrdefs.h,
hard to say if it's much cleaner than munging #ifdef's in Python code...

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.

Previous overflow test was inadequate.

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

TODO: Make the module #ifdef'ed.

This adds support for almost everything (the comma isn't currently
supported).

The "unspecified" type with floats also doesn't behave exactly like
python.

Tested under unix with float and double
Spot tested on stmhal

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

Fixed modulo operator on ints and mp ints to agree with python. Added intdivmod.c and tests/basics/modulo.py.

MICROPY_ENABLE_FLOAT is automatically set in mpconfig.h if MICROPY_FLOAT_IMPL
is set to a non-zero value.

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).

Implement not, shl and shr in mpz library.  Add function to create mpzs
on the stack, used for memory efficiency when rhs is a small int.
Factor out code to parse base-prefix of number into a dedicated function.

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

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.

Done by introducing another factored out helper API in binary.c. This API
can be reused also by array and struct modules.

The problem manifests itself in make 4.0

I also fixed the LINK message when linking the final executable for unix and unix-cpy.