access C structures via a camlp4 extension

Cstruct is a library and syntax extension to make it easier to access C-like structures directly from OCaml. It supports both reading and writing to these structures, and they are accessed via the Bigarray module.

An example pcap description is:

cstruct pcap_header { uint32_t magic_number; ( magic number *) uint16_t version_major; ( major version number ) uint16_t version_minor; ( minor version number ) uint32_t thiszone; ( GMT to local correction ) uint32_t sigfigs; ( accuracy of timestamps ) uint32_t snaplen; ( max length of captured packets, in octets ) uint32_t network ( data link type *) } as little_endian