model: Added factories for the different kinds of Units.

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>
brewnit: Parser ready to use

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>
brewnit: Added phase for literal entities in beer files

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>
brewnit: Added unit build phase for beer files

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>
brewnit: Added visitor for Fermentables

Signed-off-by: Lucas Bajolet <lucas.bajolet@gmail.com>