Support for microphone

[denis-stepanov]

It should be fairly straightforward to add a support for a regular analog mike input, as this is supported natively by Dejavu. The huge disadvantage of this input is that AdVent will only be able to mute but not unmute, so unmute will have to be done manually or on some timeout (see issue #10). The quality of recognition will probably also be not as good as with digital inputs. But the huge advantage is that no extra connection to a TV-set is needed, just putting a Pi next to it. So it might be of interest for some uses.

[denis-stepanov]

Good enough and tested locally. Manual updated. Resolving.