Added a draft version of the type checker with type inference

A datatype 'context' with a global context (class_table, featura_table, assertion_table, ...)
and stack local context has been added to the system which is already partially in use.

The type checker has not yet been activated, just included into the package.

	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
Clean up of 'eiffelc.ml'

The parsing of arguments is now done in a separate function and not
in the main function of 'eiffelc.ml'.

	modified:   ocaml/eiffelc.ml