Now MuCString is a (const char*).  It has always been intended
that MuCString instances are not to be modified.  This change just makes
it explicit in the type.

muapiparser.py just ignores the const qualifier.

Updated muapiparser.py to handle all pragmas internally.

In the text form, the NZCV flags are optional, so existing programs
are still valid. In the bundle building API, `new_binop` remain
unchanged, but an additional function `new_binop_with_status` is added,
so existing programs are still valid.

scripts/*.py are modified to adapt the MuBinOpStatus enum type.

Given all arguments (including all type arguments, signature arguments
and value arguments), the micro VM always knows how many results an
instruction has.

Fixed a bug where the last param of new_thread_nor should be
MuArraySize.

Removed MuIRNodeRefValue to make MuIRNode unique.

muapi.h also includes the common instruction names in the comment after
the macro. Improved the API parser for this purpose.

Now the IR Builder API is also available as common instructions. We keep
muapi.h as the canonical definition, and the semantics of common
instructions maps to that of the API functions.

Improved the annotations in muapi.h so that it is easier to generate
language bindings automatically.

The muapiparser.py is copied from refimpl2 for convenience.

The 'irbuilderref' type is no longer used. 'irnoderef' is the only newly
introduced Mu type. A bundle node now works as a namespace. All other
nodes are children of the bundle node. After a bundle node is loaded
into Mu (or aborted), Mu may de-allocate the bundle node and all of its
children for space efficiency.