Add SignalRouter to replace make_signal_handler and connect_signal_handler

[idanarye]

I ended up not using using fluent interface to connect multiple signals like I suggested in #11, because actions and widgets have separate connect_local methods that do not originate from the same trait. We probably bridge this with our own trait, but I'm not sure how I feel about doing so. At any rate it's not like connect_signal_handler could do it, so we are not losing functionality (sugar, actually) here.

Once this gets merged, I want to start closing the version. This mostly means bringing the docs and the tests (and the changelog - but this should not be that much work...) up to date, filling the missing parts when necessary. #5 and #7 will have to wait for 0.3 - 0.2 was delayed for long enough.

[idanarye]

@piegamesde - what do you think about this syntax?

[piegamesde]

because actions and widgets have separate connect_local methods that do not originate from the same trait.

Objection :) I've checked again and for me, both originate from GlibObject.

(I'll have a look at the code some other time.)

[idanarye]

Could have sworn I looked at it, and somehow I missed it...

I'll add connect.

[idanarye]

Time's up. I'm merging. We can always change this later.