Feature request: Add output config

[HazelHex]

Hello and thank you for i3bar-river! It would be nice to have the ability to select on which outputs the bar is visible, and on which it is not. For example, I have a very busy conky-generated bar status, which is actually needed only on the main monitor. I also have one monitor set vertically, where my bar simply does not fit, and just taking screen space there. I believe it is very useful feature which is fairly easy to implement. Thank you once again!

[MaxVerevkin]

I have some plans for a per-output override system. Something like:

[output.'output name`]
enable = false

[output.'another output']
height = 20
position = "bottom"

Let me know if you would like to work on this feature and feel free to ask for questions/directions. It can be implemented incrementally, for example enable might be the only supported option in the initial implementation. If not, I will eventually implement this, but I'm not sure when.

[MaxVerevkin]

Implemented in 1af0661

[HazelHex]

Much respect!