Update according to Contributors library guidelines

[JordanMartinez]

This pull request is part of an effort to update and standardize the Contributors libraries according to the Library Guidelines. Specifically, it:

1. Adjusts the files and repository structure according to the repository structure section of the guidelines, which includes standard pr templates, issue templates, CI in GitHub Actions, automatic stale issue management, ensures the project uses Spago, and so on.
2. Updates the README and documentation according to the documentation section of the guidelines. This is a first step towards ensuring Contributors libraries have adequate module documentation, READMEs, a docs directory, and tests (even if just usage examples) in a test directory.
3. Updates labels where relevant to help folks better sift through issues on this library and get started contributing.

This PR is the groundwork for followup efforts to ensure contributor libraries are kept up-to-date, documented, tested, and accessible to users and new contributors.

[thomashoneyman]

@JordanMartinez Do you mind using freet (or FreeT, if you'd like) as the package name instead of 'purescript-freet'? There are only a few places it's used in the README files, so it would be a quick update. Otherwise this looks good!

[JordanMartinez]

I'll use freet.

[thomashoneyman]

I think we ought to refer to packages without prefixes; while purescript- was in there originally for disambiguation in the Bower registry, it's not used in Spago and as a whole our tooling is moving towards dropping the prefix except for repository names themselves.

[JordanMartinez]

I think we ought to refer to packages without prefixes; while purescript- was in there originally for disambiguation in the Bower registry, it's not used in Spago and as a whole our tooling is moving towards dropping the prefix except for repository names themselves.

Gotcha. That makes more sense now.

[JordanMartinez]

Done.