Setup for use *as* a GitHub action

[alerque]

I would like to suggest setting this repository up so that it can be used as a GitHub action. This would involve a yaml config file for the action and a Dockerfile that sets up a copy of VIM + NeoVIM (configurable?) and this plugin and makes it easy to run against a vim plugin repository (i.e. setup the rtp etc.)

I see a lot of projects struggling with how do manage this in CI jobs. It can be done (for example see one of my implementations here) but all that boiler plate could basically be done on this side leaving the project with a one liner to run their test suite.

I realize maintenance is pretty low right now, but per #221 I am suggesting migrating this plugin to the @preservim org. This is one thing I would be able to contribute it if were migrated. Alternatively if somebody is going to commit to reviewing and merging PRs I would be happy to submit it here too. Finally it could be setup as a third party repository that basically wraps this one, but I do not think that is ideal.