Added support for initializing and terminating ME FMUs

[modelonrobinandersson]

• Change log ? I am also open to wait with this until more FMI3 functionality is in place.
• FMIL external needs to be updated since this only works with FMIL master
• Implement terminate function, reviewer can still review the rest.

[PeterMeisrimelModelon]

Looks great thus far. Aside from the comments a few things we should also add here:

• explicit free_instance function + accompanied appropriate test.
• fmi3_import_destroy_dllfmu & fmi3_import_free_instance call in __dealloc__. See FMI2 for the various occurrences of _allocated_dll and _allocated_fmu.
• [Optional] Related to terminate, some tests for valid/invalid call sequences, e.g., double termiante is not valid, and the FMU will only "midly" complain, not sure if this should be an error on the PyFMI side though

[modelonrobinandersson]

Looks great thus far. Aside from the comments a few things we should also add here:

• explicit free_instance function + accompanied appropriate test.
• fmi3_import_destroy_dllfmu & fmi3_import_free_instance call in __dealloc__. See FMI2 for the various occurrences of _allocated_dll and _allocated_fmu.
• [Optional] Related to terminate, some tests for valid/invalid call sequences, e.g., double termiante is not valid, and the FMU will only "midly" complain, not sure if this should be an error on the PyFMI side though

@PeterMeisrimelModelon see d9ae5a4 and 6e58cb5