Add monitoring of input ports

[peterfab9845]

This PR adds the ability to "monitor" input ports, similar to the way jack_capture makes its connections.
Specifically, if an input port is matched as the first pattern, then each of the output ports connected to that input port will be connected to the input port matched in the second pattern.

The easiest demonstration is likely visual:

First, jack-matchmaker 'system:playback_1' 'simple:input' was started. Then, the simple device was registered.
Upon registration, jack-matchmaker connected its input port to the same input ports as system:playback_1.

I have code stashed to add a callback for new connections, so that they get captured also; however, this causes a new refresh to happen each time the connections are updated by jack-matchmaker as well. Additionally, monitoring the removal of connections to match would be a much more significant change.

[peterfab9845]

On the other hand, it could be confusing if new connections are only copied when a new device appears. Related to #19

[SpotlightKid]

Sorry that it took ages to look at this.

Looks good in principle, but this covers only part of the needed functionality to make this really useful, IMO. New connections need also to be watched, so that when new connections to the input port in the first pattern are made, these will also trigger a new connection from the source port to the input port(s) matched by the second pattern.

But I will merge this now and ad that later.