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.

Takes slice object and sequence length and computes subsequence indexes
for case of slice step=1.

TODO: Decide if we really need separate bytecode for creating functions
with default arguments - we would need same for closures, then there're
keywords arguments too. Having all combinations is a small exponential
explosion, likely we need just 2 cases - simplest (no defaults, no kw),
and full - defaults & kw.

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.

This is special feature for FFI.

Addresses Issue #203.

This reuses as much str implementation as possible, from this we
can make them more separate as needed.

Useful as getiter method for objects which are their own iterators, etc.

In Python, importing module several times returns same underlying module
object. This also fixes import statement handling for builtin modules.

There're still issues:
1. CPython exposes set of loaded modules as sys.modules, we may want to
do that either.
2. Builtin modules are implicitly imported, which is not really correct.
We should separate registering a (builtin) module and importing a module.
CPython keeps builtin module names in sys.builtin_module_names .

Exceptions know source file, line and block name.

Also tidy up some debug printing functions and provide a global
flag to enable/disable them.

Byte code has a map from byte-code offset to source-code line number,
used to give better error messages.

So far, only storage, initialization, repr() and buffer protocol is
implemented - alredy suitable for passing binary data around.

mp_obj_int_get() can be used when just full resolution of C machine_int_t
is required (returns truncated value of long int). mp_obj_int_get_checked()
will throw exception if Python int value not representable in machine_int_t.

Change state layout in VM so the stack starts at state[0] and grows
upwards.  Locals are at the top end of the state and number downwards.
This cleans up a lot of the interface connecting the VM to C: now all
functions that take an array of Micro Python objects are in order (ie no
longer in reverse).

Also clean up C API with keyword arguments (call_n and call_n_kw
replaced with single call method that takes keyword arguments).  And now
make_new takes keyword arguments.

emitnative.c has not yet been changed to comply with the new order of
stack layout.