Added a draft version of the type checker with type inference

	modified:   library/kernel/boolean.e
	modified:   ocaml/feature_table.ml
	modified:   ocaml/feature_table.mli
	modified:   ocaml/makefile
	new file:   ocaml/signature.ml
	modified:   ocaml/support.ml
	modified:   ocaml/term.ml
	new file:   ocaml/typer.ml
	renamed:    local_context.ml -> local_ass_context.ml
	renamed:    local_context.mli -> local_ass_context.mli
	modified:   prover.ml
	new file:   ocaml/context.ml