feat: enable use of markup in clock module formats

[Dridus]

hello! this PR makes a simple change to allow the use of pango markup in clock formats. the plain label module does this, so I figured it wouldn't be out of place.

I read in the contributing guidance to open an issue or discussion as best practice, but since this is so small and I wanted it for myself I figured I'd just go straight to PR and I can close or revise it as you like.

thanks for writing ironbar!

[JakeStanger]

Thanks for the PR, agreed this makes sense to enable.

That particular contribution guideline is more for your own benefit, so that you don't spend time developing something that ultimately gets rejected. I appreciate you reading and otherwise sticking to the guidelines though :)

A couple of small changes please:

• Since the clock module also offers format_popup, could you also enable pango there to keep things consistent?
• Could you please update the clock module docs page to mention that markup is supported in each row of the config table?

I've got 0.14.1 hopefully going out this weekend, which'll be a bugfix only update. This can then follow after that and will likely be the first feature of 0.15.0.

[Dridus]

@JakeStanger okay, those changes should be made. I also made the format one match the format_popup one in terms of using LabelBuilder, to be consistent. if it should be consistently not using builder or inconsistent though let me know.

[JakeStanger]

Thanks, lgtm. Consistency with the builder interface is definitely better.

If you can just squash down the commits pls, I think this is good to go.

[Dridus]

I realized that I flubbed the squash somehow, so I corrected it in the second force-push.

[JakeStanger]

First feature of 0.15, cheers for your work on this :)