We're not going to implement all the plethora of types in there in C.
Funnily, CPython implements defaultdict in C, and namedtuple in Python.

These largely duplicate str() & bytes() constructors' functionality,
but can be used to achieve Python2 compatibility.

unix: Enable modffi by default.

Improved the Thumb assembler back end.  Added many more Thumb
instructions to the inline assembler.  Improved parsing of assembler
instructions and arguments.  Assembler functions can now be passed the
address of any object that supports the buffer protocol (to get the
address of the buffer).  Added an example of how to sum numbers from
an array in assembler.

ffi is needed to use micropython-lib, so let's have it enabled by default,
then folks who have troubles with libffi can disable it, instead of everyone
doing manual actions again and again.

This is necessary to catch all cases where locals are referenced before
assignment.  We still keep the _0, _1, _2 versions of LOAD_FAST to help
reduced the byte code size in RAM.

Addresses issue #457.

Small fixes to get it compiling with ARMCC.  I have no idea why
category_t was in the enum definition for qstrs...

This helps with handling "recursive" imports in sane manner, for example
when foo/__init__.py has something like "from foo import submod".

unix: Fix GC not tracing .data

I'm pretty sure these are never reached, since NOT_EQUAL is always
converted into EQUAL in mp_binary_op.  No one should call
type.binary_op directly, they should always go through mp_binary_op
(or mp_obj_is_equal).

With new order of evaluation of defaults, creating the tuple was done in
the wrong spot.