Cleanup project

[vemv]

Various things I did in preparation for #10. I tried to keep every commit semantic and reviewable on its own. They go as follows:

• Remove unused ring/ring-devel
• Mark :test dependencies as such
  • This tends to be cleaner - it's the "deps.edn" way, which we can follow even when using Lein :)
• :test-selectors: default to running all tests
  • This is safer, especially for the CI integration.
• Setup logging
  • This silences Jetty logging, which can be otherwise noisy, especially when using the :port 0 option.
• Satisfy clj-kondo and Eastwood
• Use randomized ports in tests
  • This yields an overall cleaner pattern, avoiding a defonce, possible interference with other processes, etc.
• Remove some commented-out tests
  • Persistent HTTP connections are not supported (per Readme.md)
• Enable test exercising :insecure? again
• Remove references to unsupported :multipart option
  • Closes Documentation has examples for multipart requests but they don't seem to work #5
• Set up a test matrix
  • I tentatively changed the CI to Circle since it's better maintained and offers a native matrix syntax. Build is green in my account:

[vemv]

@martinklepsch: looking good?

[martinklepsch]

Looking good indeed @vemv! Sorry for the delayed response here :)

[martinklepsch]

Indentation :)

[vemv]

Whoops! Amended

[martinklepsch]

I added you as a collaborator to this project. Please go ahead and merge this PR as your first action as a co-maintainer :)

[vemv]

Thanks! 🍻

I realised a bit too late that the .circleci file was redundant (in this PR I had noticed the Travis file but not the GH Actions file). Removed in master, improved the GH Actions as well to use a matrix