Add peakusage

[dupondje]

As the new Fluvius DSMR Standard (V1.7.1) now also returns peak values and a history of them, this needs to be added to the DSMR parser.

This pull request does this :)

Please comment. But I implemented the test, and it works fine :)

[dupondje]

@ndokter: Could you check and merge? :)
@dennissiemensma: Maybe you can test it in DSMR Reader?

[ndokter]

Thanks for your hard work. I've merged the changes and will make a new build soon (within 2 weeks)

You too @dennissiemensma! Although i'm not entirely sure if i already want to remove 3.6 support yet

[dennissiemensma]

@dupondje

@dennissiemensma: Maybe you can test it in DSMR Reader?

Thanks! I'll check it whenever I'll work on dsmrreader/dsmr-reader#1764.

DSMR-reader uses a kind of forked version, but I still update it every now and then when there is a good reason to (now there is).

[dennissiemensma]

@ndokter

You too @dennissiemensma! Although i'm not entirely sure if i already want to remove 3.6 support yet

It's entirely up to you. There is no right or wrong.

If I may give some unasked advise, you can use semver to solve these issues. Just bump the major version of your package and drop end-of-life versions of Python (and dependencies) in it.
This way you both hint users of your package that they should bump their Python version and it allows you to (eventually) use features of later Python versions. But the best side-effect is that even if users do not want or can upgrade their Python version: They can just pin the previous major of your package.