V2: Initial API

[jwijenbergh]

This PR refactors the public API by exposing a JSON API instead of handing over C types. This greatly simplifies the codebase

Also fixes #3, #10, #12, #15

TODO:

• [x] Document API
  • [x] comments in exports
  • [x] High level + tutorial https://jwijenbergh.github.io/eduvpn-common
  • [x] Add back python example
• [x] Use an enum instead of "secure_internet", "institute_access", "custom_server"
• [ ] Cleanup conversion functions in client package
• [x] Split types into several packages
• [x] Make tests pass