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.
En fait, dans ce cas on ne veut pas suivre la covariance car on ne saurait pas quel type précis déserialiser par après.