Deserialize generics with nitserial

nitserial compiles a Nit module after analyzing a Nit program. This module can then be compiled with the program (possibly using `-m`) to support deserializing any alive generic type. Many generated module can be used to support different libraries with hidden serialization logic, or to support exchanges between a client and a server.

Will be used by the RESTful interface of Benitlux.
et opt_dir ?