2.2.0 - Major internal refactor

Kong certbot agent has proved way more popular than I thought it would be, and a number of small but breaking problems have been creeping up as Kong approaches its v1.0 release. There was a need for more quality control, or rather, for quality control (period).

This version brings a major internal refactor to allow for a good battery of tests to be run against any code changes. I've found a myriad of small issues while doing this and hopefully fixed others. The new tests will make it way easier to fix and change stuff in the future.

This is just a minor version bump (from 2.1.x to 2.2.0) though as it's 100% backwards compatible with both command line and Kong 0.14.

Changes:

• Split code into different concerns
• Test each concern separately
• Test the whole app as a function
• Add to CI
• Add coverage metrics
• Ensure contributor's fixes are all in
• Fix:
  • Certificate collisions
  • Error resiliance during collisions - now certs can be saved per domain when this happens
  • Error reporting