Allows to have nested try blocks with except filters.

TODO: Don't add END_FINALLY's exception re-raise points to traceback.

Implement __bool__ and __len__ via unary_op virtual method for all types.

__bool__() and __len__() are just the same as __neg__() or __invert__(),
and require efficient dispatching implementation (not requiring search/lookup).
type->unary_op() is just the right choice for this short of adding
standalone virtual method(s) to already big mp_obj_type_t structure.

To alloc complete memory alloc flow tracing.

We still have FAST_[0,1,2] byte codes, but they now just access the
fastn array (before they had special local variables).  It's now
simpler, a bit faster, and uses a bit less stack space (on STM at least,
which is most important).

The only reason now to keep FAST_[0,1,2] byte codes is for compressed
byte code size.

LOAD_METHOD bug was: emitbc did not correctly calculate the amount of
stack usage for a LOAD_METHOD operation.

small int bug was: int was being used to pass small ints, when it should
have been machine_int_t.

* Add SD card test to fix warning

* Remove include mpconfigport.h from file.c

* Issue #232

On my machine, 'import array' in CPython tries to load the array test.

unix: Initial FFI module implementation

Foreign Function Interface module allows to load native dynamic libraries,
call functions and access variables in them. This makes possible to write
interface modules in pure Python.

This module provides thin wrapper around libffi. ctypes compatibility might
be possible to implement on top of this module (though ctypes allow to call
functions without prototypes, which is not supported by libffi (i.e.
implementation would be inefficient))).

This is special feature for FFI.

Fixed '#ifdef's so Linux would compile again and added
.scl and .type for Windows.

Fix implicit double conversion warning