Working towards trying to support compile-time constants (see discussion
in issue #227), this patch allows the compiler to look inside arbitrary
uPy objects at compile time.  The objects to search are given by the
macro MICROPY_EXTRA_CONSTANTS (so they must be constant/ROM objects),
and the constant folding occures on forms base.attr (both base and attr
must be id's).

It works, but it breaks strict CPython compatibility, since the lookup
will succeed even without importing the namespace.

Can do this now that the stack size calculation is improved.

Much less of a hack now.  Hopefully it's correct!

Labels should never be negative, and this modified type signature
reflects that.

Needed to reinstate 2 delete opcodes, to specifically check that a local
is not deleted twice.

So we can add more flags.

Small reduction in ROM, heap and stack usage.

Convert int types to uint where sensible, and then to uint8_t or
uint16_t where possible to reduce RAM usage.

On x64, native emitter now passes 70 of the tests.

Also add command line option to unix port to select emitter.

Previous overflow test was inadequate.

Very little has changed.  In Python 3.4 they removed the opcode
STORE_LOCALS, but in Micro Python we only ever used this for CPython
compatibility, so it was a trivial thing to remove.  It also allowed to
clean up some dead code (eg the 0xdeadbeef in class construction), and
now class builders use 1 less stack word.

Python 3.4.0 introduced the LOAD_CLASSDEREF opcode, which I have not
yet understood.  Still, all tests (apart from bytecode test) still pass.
Bytecode tests needs some more attention, but they are not that
important anymore.

Don't store final, failing value to the loop variable.  This fix also
makes for .. range a bit more efficient, as it uses less store/load
pairs for the loop variable.

These are default arguments after a bare *.

In preparation for implementing default keyword arguments.

The way it is, just crashes app. And optimizing to
"raise ZeroDivisionError" is probably too much.

Eg class A(): pass would fail an assertion.

Mostly just a global search and replace.  Except rt_is_true which
becomes mp_obj_is_true.

Still would like to tidy up some of the names, but this will do for now.

Partly (very partly!) addresses issue #386.  Most importantly, at the
REPL command line, each invocation does not now lead to increased memory
usage (unless you define a function/lambda).

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

Remove unnecessary includes. Add includes that improve portability.

Checks for non-default args following default args, and errors out.
Addresses issue #328.