Allow mutating generator functions for points

[Dr-Emann]

This allows for additional flexibility for the caller, for example, code in the form of:

buffer = [f(), f(), f(), ..];
point = Point::generate(|i| buffer[i])

can be replaced with

point = Point::generate(|_| f())

[adamreichold]

The change to change log format seems unrelated should probably land in a separate PR?

[Dr-Emann]

Sure, I can move it into another PR. Where should I put the changelog entry for this unreleased version in this PR? Should I make a new "unreleased" section more closely matching the original format, and put it there, or make a new 0.9.0 section?

[urschrei]

@Dr-Emann Apologies for the long delay. We (georust) have taken over stewardship of this crate in order to facilitate maintenance and feature dev. If you're still interested, we'd like to get this merged – if you could rebase against master and update the changelog, we should be good to go.

[Dr-Emann]

Since it's a breaking change, should I change the changelog to be for 0.9.0?

[urschrei]

Sure!

[Dr-Emann]

Rebased on master

[michaelkirk]

bors r+

[bors[bot]]

Build succeeded:

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