Remove unnecessary includes. Add includes that improve portability.

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).

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.

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.

Only works on modules and class instances.

Can now have null bytes in strings.  Can define ROM qstrs per port using
qstrdefsport.h

Currently, MicroPython strings are mix between CPython byte and unicode
strings. So, conversion is null so far. This dummy implementation is
intended for compatibility with CPython (so, same code can run on both).

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.

Made sorted() raise an exception instead of aborting when given no arguments; moved around some things in objfun.c as a consequence

Creating of classes (types) and instances is much more like CPython now.
You can use "type('name', (), {...})" to create classes.

Addresses issue #104.

Now much more inline with how CPython does types.

Qstr's are now split into a linked-list of qstr pools.  This has 2
benefits: the first pool can be in ROM (huge benefit, since we no longer
use RAM for the core qstrs), and subsequent pools use m_new for the next
pool instead of m_renew (thus avoiding a huge single table for all the
qstrs).

Still would be better to use a hash table, but this scheme takes us part
of the way (eventually convert the pools to hash tables).

Also fixed bug with import.

Also improved the way the module code is referenced (not magic number 1
anymore).

import works for simple cases.  Still work to do on finding the right
script, and setting globals/locals correctly when running an imported
function.

A big change.  Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object).  This scheme follows CPython.  Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.

Also change name prefix, from py_ to mp_ (mp for Micro Python).