This completes non-automatic interning of strings in the parser, so that
doc strings don't take up RAM.  It complicates the parser and compiler,
and bloats stmhal by about 300 bytes.  It's complicated because now
there are 2 kinds of parse-nodes that can be strings: interned leaves
and non-interned structs.

MP_ALLOC_* -> MICROPY_ALLOC_*
MICROPY_PATH_MAX -> MICROPY_ALLOC_PATH_MAX
MICROPY_ENABLE_REPL_HELPERS -> MICROPY_HELPER_REPL
MICROPY_ENABLE_LEXER_UNIX -> MICROPY_HELPER_LEXER_UNIX
MICROPY_EXTRA_* -> MICROPY_PORT_*

See issue #35.

bytecode is the more widely used.  See issue #590.

You can now do:

    X = const(123)
    Y = const(456 + X)

and the compiler will replace X and Y with their values.

See discussion in issue #266 and issue #573.

Just a start, no working code yet.  As per issue #573.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

It's the same as LOAD_CONST_STR.

Messages are still explanatory, while taking a little less ROM.

New way uses slightly less ROM and RAM, should be slightly faster, and,
most importantly, allows to catch the error "non-keyword arg following
keyword arg".

Addresses issue #466.

Implements 'def f(*, a)' and 'def f(*a, b)', but not default
keyword-only args, eg 'def f(*, a=1)'.

Partially addresses issue #524.

Also add a few STATIC's to some compile functions that should have them.

Addresses issue #521.

Closed over variables are now passed on the stack, instead of creating a
tuple and passing that.  This way memory for the closed over variables
can be allocated within the closure object itself.  See issue #510 for
background.

mp_obj_t->subscr now does load/store/delete.

Attempt to address issue #386.  unique_code_id's have been removed and
replaced with a pointer to the "raw code" information.  This pointer is
stored in the actual byte code (aligned, so the GC can trace it), so
that raw code (ie byte code, native code and inline assembler) is kept
only for as long as it is needed.  In memory it's now like a tree: the
outer module's byte code points directly to its children's raw code.  So
when the outer code gets freed, if there are no remaining functions that
need the raw code, then the children's code gets freed as well.

This is pretty much like CPython does it, except that CPython stores
indexes in the byte code rather than machine pointers.  These indices
index the per-function constant table in order to find the relevant
code.

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

This simplifies the compiler a little, since now it can do 1 pass over
a function declaration, to determine default arguments.  I would have
done this originally, but CPython 3.3 somehow had the default keyword
args compiled before the default position args (even though they appear
in the other order in the text of the script), and I thought it was
important to have the same order of execution when evaluating default
arguments.  CPython 3.4 has changed the order to the more obvious one,
so we can also change.

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.