Release v2.1.0

[oseasandrepro]

Formalize interface definition language and data definition language.
The idia hers is: since SRPC use Python as IDL all content of <module_name>_interface.py and <module_name>.py must use type hint mandatorily.

Check below a consistent and correct interface file content:

from abc import ABC, abstractmethod

class CalcInterface(ABC):
    @abstractmethod
    def add(self,  a: int, b: int) -> int:
        pass

    @abstractmethod
    def sub(self, a: int, b: int) -> int:
        pass

    @abstractmethod
    def mult(self, a: int, b: int) -> int:
        pass

    @abstractmethod
    def div(self, a: int, b: int) -> float:
        pass