This is a one-liner fix.  It gets the class-super.py test passing, but
is probably not a complete fix.

Also, checked that both bytearray and array.array actually support generic
(a-la list) slice assignment and deletion. Added TODOs.

No logic changes, just coding style to make it easy to read.

3 emitter functions are needed only for emitcpy, and so we can #if them
out when compiling with emitcpy support.

Also remove unused SETUP_LOOP bytecode.

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.

Avoids pointer-to-field garbage collection issue. Fixes #510.

There were typos, various rounding errors trying to do concurrent counting
in bytes vs blocks, complex conditional paths, superfluous variables, etc.,
etc., all leading to obscure segfaults.

Useful as callback data, etc.

These are to assist in writing native C functions that take positional
and keyword arguments.  mp_arg_check_num is for just checking the
number of arguments is correct.  mp_arg_parse_all is for parsing
positional and keyword arguments with default values.

When querying an object that supports the buffer protocol, that object
must now return a typecode (as per binary.[ch]).  This does not have to
be honoured by the caller, but can be useful for determining element
size.

We are not as verbose as CPython, and maybe a bit too cryptic sometimes.

Test usecase I used is print(time.time()) and print(time.time() - time.time()).
On Linux/Glibc they now give the same output as CPython 3.3. Specifically,
time.time() gives non-exponential output with 7 decimal digits, and subtraction
gives exponential output e-06/e-07.

I skipped implementing this initially, but then it causes __name__
of current module be overwritten and relative imports fail.

On stmhal, computed gotos make the binary about 1k bigger, but makes it
run faster, and we have the room, so why not.  All tests pass on
pyboard using computed gotos.

Also make consistent use of MP_OBJ_NOT_SUPPORTED and MP_OBJ_NULL.
This helps a lot in debugging and understanding of function API.

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

With this fix, all tests in tests/basics pass on pyboard.

I.e. with its own globals. So, just as for functions, we need to switch
globals when resuming a generator.