EverParse3d: verified message validation with dependent data
descriptions

Contents:

* ./*.fst, ./*.fsti: the F* source code of the 3d.exe executable that
  takes 3D data format descriptions and generates F* format
  definitions with the 3D AST along with corresponding interpreter
  calls and partial evaluation directives for verified validators.

* ocaml/*.ml*: the OCaml stubs for the implementation of 3d.exe

* ocaml/generated: the OCaml implementation of 3d.exe generated from
  F* sources.

* prelude: the F* theories for verified parser and validator
  combinators, actions, and the interpreter. (See prelude/README)

* tests: some tests, including TCP/IP (see tests/tcpip/README)
