Use a build script

[sts10]

Theoretically, this will make runtime faster.

PR takes instruction from: Rust docs and Pgen.

[sts10]

In actual benchmarks with Hyperfine...

hyperfine --setup 'cargo install --force --path=.' -w 2000 -m 3000 -N phraze

This PR is about even with the main branch, which does not use a build script. Kind of a bummer! That said, with either setup we're averaging 1.5 ms, so not bad.

Note: pgen runs in a mean of 1.3 ms on my machine, but I'm not worried.

[sts10]

Well, turns out that by using Criterion, we see that the method of using a build script is about 500x faster, so I've merged this branch.