nitdbg: Added module debugger

Signed-off-by: Lucas BAJOLET <r4pass@hotmail.com>
nitdbg: Added capacity to interpret with debugger in nit.nit

Signed-off-by: Lucas BAJOLET <r4pass@hotmail.com>
nitdbg: Added a new function to get an attribute in a MutableInstance (Complex Object)

Signed-off-by: Lucas BAJOLET <r4pass@hotmail.com>
nitdbg: Added function to get a specific variable in a MutableInstance (recursively)

Signed-off-by: Lucas BAJOLET <r4pass@hotmail.com>