Builtin now takes two arguments: function_name and function_type

Changes to be committed:
* btl/types.typer: reflect "Builtin" change
* src/elexp.ml: unsusp susp
* src/REPL.ml:
	- reflected change linked to elexp.ml
	- file reading is now done with eval_file
* src/builtin.ml
	- add predefined_table and get_predefine
* src/lparse.ml:
	- simplified handle_call as it had a lot of legacy code
	- constructor now inherit inductive's formal_args as Aerasable arguments
		cons : (a : Type) ≡> (v : a) -> List a -> List
	- predef_table is populated in default_ctx right after
	builtin type definition were read
* src/debug_util.ml:
	- added: -typecheck argument