Implement Github Actions

[alicerunsonfedora]

This PR makes the following structural changes:

• New workflows for GitHub Actions have been added for linting and builds. These workflows also handle release asset uploads as necessary.
  • These workflows also make use of some of our custom actions, renpy-build-action and renpy-lint-action.
  • Linting runs on every push and pull request.
  • Building runs on every push and publishing artifacts runs only when releases have been
    published.
  • Building across multiple versions works via the matrix entry in the YAML files
• The inject_version script has been modified in the following ways:
  • The variables to look for are now based on env variables in Github Actions
  • Since GitHub Actions doesn't have refs and SHAs shortened like Travis, the script also handles shortening them to readable formats
  • The replacement also attaches the respective Ren'Py SDK version to prevent release conflicts
• The Travis CI YAML file and some older scripts have been removed in favor of Github Actions.

[gitpod-io-legacy-app]

Open in Gitpod - starts a development workspace for this pull request in code review mode and opens it in a browser IDE.

[sr229]

Oh by the way, think you can port this on Sayo-nika? Feel free to create a sample mod so people have an idea how to use it, this would make a good boilerplate for both private and public projects.

[alicerunsonfedora]

I think this is somewhat portable since we already have custom Github Actions that are used that are publicly available.

https://github.com/ProjectAliceDev/renpy-build-action
https://github.com/ProjectAliceDev/renpy-lint-action