Implemented dependency resolution.

now we have 4 passes: fast_inst_sel, fast_reg_alloc, followed
by slow_inst_sel and slow_reg_alloc. This might make the
compilation pipeline more linear

Creaation and destruction of MuVM, MuCtx and MuIRBuilder. Now the
`mvm->new_context`, `ctx->new_ir_builder`, `ctx->close_context` and
`b->abort` works. MuVM can also be created via a top-level "C"-style
exported function `mu_fastimpl_new()` so that in theory, it can be used
in C programs.

internal id and machine id do not persist during serialization
and restoration. Currently I use fixed ID for machine registers.
But internal id is still generated, this might be a problem in
the future.

Now it is the time to actually implement the public API. This commit
only contains scaffolds so that it compiles, and I can fill in actual
implementations later. Most of them should forward to the actual VM.*
methods (with some adaptations).

Found a way to implement handle allocation and dealllocation, and a way
to access MuVM from MuCtx using pointers.

Re-wrote the muapi2rustapi.py script.

Use *const for CStrings and CMuValue.

Set linker flags properly according to the OS.

Tested trap handler callback. It looks like it is easy enough for Rust
to interact with C.

Added linker flags so it will work in Linux.

Test whether the generated stubs are reasonable.