Generate kqueue bindings

[leostera]

One of the first interesting goals for ocaml-bidngen is to generate bindings for the kqueue set of syscalls, so we can drop the custom C code we have in gluon.

At minimum we need a module that implements these:

• Creating a new kqueue instance: kqueue : unit -> kqueue
• Polling for events on a kqueue instance: kevent : max_events:int -> timeout:int64 -> kqueue -> event array
• Updating the kqueue instance: fcntl : Fd.t -> cmd:int -> arg:int -> int
• Registering events of interest: kevent_register : kqueue -> event array -> int array -> unit

The current custom C code for this lives here.