The main purpose of this PR is to remove the `'static` lifetime bound in

type OpCreator =
  fn(state: &Arc<IsolateState>, base: &msg::Base, data: &'static mut [u8])
    -> Box<Op>;

The reason is simple: it is plain wrong, the `data` is actually not `'static`. It is created when the message is sent from C side, and will be recycled when the message is responded. It violates the definition of `'static` lifetime.

If someone save this pointer somewhere else, and reuse it later again, uninitialized memory could be accessed. This kind of memory unsafety does not happen yet because the logic is carefully organized in this project. Lifetime constraints are maintained by code convention. It could be more robust if we can express this constraint by Rust's type system.

Basic idea: tie buffer's lifetime to an object's lifetime, a.k.a, RAII. The type `deno_buf` is pretty suitable for this job.