Generic piecewise function trait and impls

pcw_fn is a library for handling piecewise defined functions (or other "piecewise data") generically.

Currently the PcwFn trait the library is built around is implemented for a single type: VecPcwFn. This type represents a piecewise function f given by a collection of jump positions and functions such that

       ╭ f₁(x)   if      x < x₀
       │ f₂(x)   if x₀ ≤ x < x₁
f(x) = ┤ f₃(x)   if x₁ ≤ x < x₂
       │  ⋮               ⋮
       ╰ fₙ(x)   if xₙ ≤ x

for all x ∈ X where f₁,...,fₙ : X -> Y, and x₀ < x₁ < ... < xₙ from some strictly totally ordered set X (so X is Ord). Note that for most functionality it's not required that the funcs actually behave like a function so the type can be used very well for "non-functional" funcs.

It's trivial to add impls backed by other types like SmallVec or StaticVec.

License

^{Licensed under either of Apache License, Version 2.0 or MIT license at your option.}
_{Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.}