binary sensors opto_in are not implemented

[litinoveweedle]

Hello, as title says, binary sensors for optical inputs are not implemented. This is probably caused by the missing implementation of the corresponding get_opto_in methods in the python library, where only get_all_opto() is implemented which is currently not directly usable via simple get command reference in the data.py.

Will you accept PR for multiio library extending support for get_opto_in(channel) method, so then optical binary sensors could be implemented in the SMmultiio-ha data.py?

Or do you prefer to implement per channel logic in the SMmultiio-ha directly?

[litinoveweedle]

Checking python library I found that it contains get_opto implementation, so only its documentation in the README is missing.

    def get_opto(self, channel):
        """Get optocoupled input status. 

        Args:
            channel (int): Channel number

        Returns:
            (bool) Channel status
        """
        self._check_channel("opto", channel)
        opto_mask = self._get_byte(I2C_MEM.OPTO)
        if(opto_mask & (1 << (channel - 1))):
            return True
        else:
            return False

[litinoveweedle]

Proposed in PR #4