Also resolves dependency

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.

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).

api_bridge.rs will convert low-level C valus to high-level Rust value,
such as CMuValue* -> [&APIMuValue].

45f4501e3855f6cdfb6b132ceac1f8ec0222cce2