Update prop.py

[pronoym99]

1. Convert format strings to python3.6+ compliant f-strings wherever possible.
2. Optimise return statements of functions having rudimentary if - else statements with equivalent boolean expressions.

[coveralls]

Pull Request Test Coverage Report for Build 3359412227

• 25 of 38 (65.79%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 93.328%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/icalendar/prop.py	25	38	65.79%

Files with Coverage Reduction	New Missed Lines	%
src/icalendar/prop.py	2	87.0%

Totals
Change from base Build 3354567871:	0.3%
Covered Lines:	1161
Relevant Lines:	1244

---

💛 - Coveralls

[pronoym99]

Please add a hacktoberfest label to this PR if possible.

[jacadzaca]

@pronoym99 Could you add yourself to the changelog and contributors list as per CONTRIBUTING?

[pronoym99]

Yes sure.

[pronoym99]

@jacadzaca Done the required changes. Please have a look.

[jacadzaca]

@pronoym99 I did, you've pushed the changes to #481

[pronoym99]

@jacadzaca bifurcated CHANGES pertaining to each of #481, #482 and #483.

[jacadzaca]

@pronoym99 Great, could you now format the changelog as I've asked and put it under the 5.0.2 version, please? Could you also squash your commits, two commits per PR seem resonable -- we don't want to pollute the log with changelog update.

[pronoym99]

@jacadzaca I have squashed the commits for this PR and updated the changelog by adding the changes in 5.0.2 as requested by you.

[jacadzaca]

@pronoym99 I think your squash didn't work since there are still 7 commits?

[pronoym99]

@jacadzaca Yes. I was doing it using the GitKraken app. I need to do so in the cmd line. Maybe it will work there.

[jacadzaca]

I'd also phrase the changelog entry differently, e.g converted all format strings into f-strings in prop.py or just refactored prop.py. The one now is a bit of a mouthful. That's up to you tho :)

[niccokunzmann]

Thanks for the PR! I left a comment. Also, this CHANGES file is quite big..

[niccokunzmann]

Thanks for your changes!