Unify property extractor function names

[grodin]

Closes #521

I'm opening this as a draft as the docs aren't updated yet and this is just supposed to be to get the bikeshedding going.

Known things to fix before merge:

• [ ] ~update docs~
• [x] update README
• [x] update CHANGELOG
• [x] update names of tests
• [x] deprecate old functions

[evant]

While we are still bike-shedding the naming I want to call out we'll want to keep but deprecate the old names, not get rid of them entirely.

[grodin]

Yeah, I realised that after I pushed those commits. I was a bit too enthusiastic to get the bike-shedding going I think.

I'll add that to the to-do list above.

[grodin]

Let me know if you want this squashed

[grodin]

I'll let you squash it