added a Main module for the interpreter;
more stuff in Typing (basic constructors, printers);
in Ast (and parser), new constructor Print, for debugging and devel
updated examples
_tags file (unix module)
update of the Prolog module (with a Clause submodule and a partial implementation, but
not quite working yet).
Env.action type, that can be obtained through Ast;
functions in Env to perform actions