Migrate to GitHub Actions

* Derive Generic instance for Either

* Remove dependency on generics-rep

Co-authored-by: Paul Young <84700+paulyoung@users.noreply.github.com>

* Generate CHANGELOG.md file using notes from previous GH releases

* Add pull request template

* Update CI in PS to v0.14.0-rc5

This is part of a set of commits that rearrange the dependencies between
multiple packages. The immediate motivation is to allow certain newtypes
to be reused between `profunctor` and `bifunctors`, but this particular
approach goes a little beyond that in two ways: first, it attempts to
move data types (`either`, `tuple`) toward the bottom of the dependency
stack; and second, it tries to ensure no package comes between
`functors` and the packages most closely related to it, in order to open
the possibility of merging those packages together (which may be
desirable if at some point in the future additional newtypes are added
which reveal new and exciting constraints on the module dependency
graph).

* Update CI to build with the latest version of the compiler

* Update the bower repository URL to match the URL in the registry

* Upgrade bower dependencies

* Update the changelog

* Update to CI to use 'unstable' purescript

* Update pulp to 16.0.0-0 and psa to 0.8.2

* Update Bower dependencies to master

* Added changelog entry

* Update the bower dependencies

* Update Node to 14 in CI

* Update the changelog

Also update docstring wording