feat(upower): add new formatting properties

[Disr0]

Adds parsing in format for properties other than {percentages} 😵‍💫

Resolves #440

[JakeStanger]

Thanks for the PR. This is definitely a good addition. There are a few small bits that I think need addressing before this goes in:

This is a new feature, not a bug fix :) Could you amend your commit message to reflect that please so it gets added to the changelog correctly. Something like: feat(upower): add new formatting properties.

I don't think adding icon_name as a property is particularly helpful, unless there's something smart you could do with this and Pango? Otherwise it's sort of an internal identifier that gets exposed with little purpose.

Arguably the time_to_empty and time_to_full properties should be combined into one (perhaps just time_remaining?), which checks the state to see which underlying property to use. Otherwise you end up having to add both to have the ETA consistently display:

{ type = "upower" format = "{percentage}% {state} ({time_to_empty}{time_to_full})" }

I'm not sure whether the combine property should be instead of or in addition to the separated ones? Would people ever want to show one and not the other? I'm open to feedback on that one.

Once that's all done I'll re-review and update the docs page. Let me know if you need any help with any of the above :)

[JakeStanger]

[Changes requested above]

[Disr0]

Yeah, icon_name isn't particularly useful, I'll remove it from the formatting.
Combining time_to_empty and time_to_full sounds more correct, yeah, but how should it be done? I'm not sure if adding if switch is a good idea, but maybe it's better than just concatenating time_to_empty and time_to_full as a string and sending it as time_remaining?

[JakeStanger]

Looking nearly there, cheers for your work on this. Just one minor adjustment I think, then I'm happy with it.

Are you able to squash your commits down into a single one which matches the PR title? I can give a hand with that if not.

[Disr0]

Should be done now

[JakeStanger]

Cheers, lgtm. I'll update the docs to add in the relevant section & merge in the next few days.