There were several different spellings of MicroPython present in comments,
when there should be only one.

Previous to this patch any non-interned str/bytes objects would create a
special parse node that held a copy of the str/bytes data.  Then in the
compiler this data would be turned into a str/bytes object.  This actually
lead to 2 copies of the data, one in the parse node and one in the object.
The parse node's copy of the data would be freed at the end of the compile
stage but nevertheless it meant that the peak memory usage of the
parse/compile stage was higher than it needed to be (by an amount equal to
the number of bytes in all the non-interned str/bytes objects).

This patch changes the behaviour so that str/bytes objects are created
directly in the parser and the object stored in a const-object parse node
(which already exists for bignum, float and complex const objects).  This
reduces peak RAM usage of the parse/compile stage, simplifies the parser
and compiler, and reduces code size by about 170 bytes on Thumb2 archs,
and by about 300 bytes on Xtensa archs.

Grammar rules have 2 variants: ones that are attached to a specific
compile function which is called to compile that grammar node, and ones
that don't have a compile function and are instead just inspected to see
what form they take.

In the compiler there is a table of all grammar rules, with each entry
having a pointer to the associated compile function.  Those rules with no
compile function have a null pointer.  There are 120 such rules, so that's
120 words of essentially wasted code space.

By grouping together the compile vs no-compile rules we can put all the
no-compile rules at the end of the list of rules, and then we don't need
to store the null pointers.  We just have a truncated table and it's
guaranteed that when indexing this table we only index the first half,
the half with populated pointers.

This patch implements such a grouping by having a specific macro for the
compile vs no-compile grammar rules (DEF_RULE vs DEF_RULE_NC).  It saves
around 460 bytes of code on 32-bit archs.

This patch moves some common code from the individual inline assemblers to
the compiler, the code that calls the emit-glue to assign the machine code
to the functions scope.

These are generic methods that don't depend on the architecture and so
can be handled directly by the compiler.

This reduces fragmentation, and memory use by 1 word.  But more
importantly it means the emit_inline_asm_t struct now "derives" from
mp_asm_base.

All assemblers should "derive" from mp_asm_base_t.

Reduces code size by 112 bytes on Thumb2 arch, and makes assembler faster
because comparison can be a simple equals instead of a string compare.

Not all ops have been converted, only those that were simple to convert
and reduced code size.

Supported return types are: object, bool, int, uint.

For example:

@micropython.asm_thumb
def foo(r0, r1) -> uint:
    add(r0, r0, r1)

movwt can now move a full 32-bit constant into a register.

Only IPSR and BASEPRI special registers supported at the moment, but easy
to extend in the future.

Contains just argument names at the moment but makes it easy to add
arbitrary constants.

As per ARM convention.

Cortex-M0, M0+ and M1 only have ARMv6-M Thumb/Thumb2 instructions.  M3,
M4 and M7 have a superset of these, named ARMv7-M.  This patch adds a
config option to enable support of the superset of instructions.

Adds support for the following Thumb2 VFP instructions, via the option
MICROPY_EMIT_INLINE_THUMB_FLOAT:

vcmp
vsqrt
vneg
vcvt_f32_to_s32
vcvt_s32_to_f32
vmrs
vmov
vldr
vstr
vadd
vsub
vmul
vdiv

This patch gets full function argument passing working with native
emitter.  Includes named args, keyword args, default args, var args
and var keyword args.  Fully Python compliant.

It reuses the bytecode mp_setup_code_state function to do all the hard
work.  This function is slightly adjusted to accommodate native calls,
and the native emitter is forced a bit to emit similar prelude and
code-info as bytecode.

Addresses issue #1143.

Addresses issue #1132.

Reduces stmhal by about 300 bytes ROM.

Also gives line number of location of error.  Very useful!

These are useful for implementing atomic lock operations.