Migrate CI from Travis to GitHub Actions

[skwashd]

Over a year and a half ago Travis dropped their support for open source projects. I ported the Travis CI job to GitHub Actions. I made a few other changes along the way to ensure the pipelines would work properly:

• One of the nonsense files was causing issues, so I removed it.
• Added a hack to work around ConfigFileFinder is removed from flake8 #33 until fix: refactor from ConfigFileFinder to load_config #35 is merged. I also stole borrowed @lsorber's other dependencies changes
• Split testing and releasing into separate actions

[skwashd]

Here is an example of the matrix build in operation - https://github.com/skwashd/flake8-bandit/actions/runs/2856412389

If at first you don't succeed, try try again!