Add an implementation of the cp32 rolling hash algorithm

[bobg]

[github-actions[bot]]

Modver result

This report was generated by Modver, a Go package and command that helps you obey semantic versioning rules in your Go module.

This PR requires an increase in your module’s major version number. If the new major version number is 2 or greater, you must also add or update the version suffix on the module path defined in your go.mod file. See the Go Modules Reference for more info.

no new version of package github.com/bobg/hashsplit/v2
  Major