CI: Proposal: Use Azure piplines
I started to implement a Azure Pipeline for the whole kaitai CI: https://github.com/cugu/kaitai_struct/tree/azure

The complete pipeline (Build Compiler, Translator Test, Build JS, Build Packages, Target Language Tests: https://dev.azure.com/cugu/dfir/_build/results?buildId=106&view=results) takes about 5:25 minutes (with caching).

Currently only Python and Ruby tests are working, but implementing more languages should not take more time, as they are tested in parallel.

I wanted to get some feedback on this before I continue. 

Proposed actions:

- [ ] Implement all tests
- [ ] Delete [ci_targets](https://github.com/kaitai-io/ci_targets) repository
- [ ] [kaitai_struct](https://github.com/kaitai-io/kaitai_struct):
     - [ ] Delete .travis.yml
- [ ] [kaitai_struct_compiler](https://github.com/kaitai-io/kaitai_struct_compiler):
  - [ ] Delete .circleci/config.yml (is this used anyway?)
- [ ] Rewrite CI documentation