A curve trait for general interoperation (#80)

* Initial commit

* Write curve-trait.md

* Rename curve-trait.md to 80-curve-trait.md

* Added `Interval`, `zip`, `sample_checked`, `sample_clamped`

* Added examples of curve applications in games

* Added commentary on borrowing and object safety

* Apply some suggestions from code review

Co-authored-by: Alice Cecile <[email protected]>

* Snippet in drawbacks about maintenance burden etc.

* Partial rewrite of user-facing introduction

* Update rfcs/80-curve-trait.md

Co-authored-by: Alice Cecile <[email protected]>

* Updates from comments

* Typo

* Rewrite to remove type-inferred interpolation from the core of the trait

* Add end-to-end composition

* Added section on shared interpolation interfaces

* Mention sample_with in exposition

* Update rfcs/80-curve-trait.md

Co-authored-by: Alice Cecile <[email protected]>

* Rename compose -> chain

* Updates to Interval methods

* Clarify that Interval is not an Iterator

* Add Interval::contains_interval for checking containment between two intervals

* Switch resample from samples to segments

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Co-authored-by: Alice Cecile <[email protected]>

Author: mweatherley