REST API and Documentation for APIs

[achimnol]

Let's add an API to Sorna so that external services can easily integrate with this code execution service.

• API Design
  • [x] Authentication like AWS API
  • [x] Standardized error response (candidate: RFC-7807)
  • [x] Kernel/session management
  • [x] Code execution and result returns in various forms (including WebSocket-based stdout streaming and customized display data)
• Backend
  • [x] Usage metrics and statistics
  • [ ] Billing
• Documentation
  • [x] Create a readthedocs site.

[achimnol]

Billing is now moved to internal project. Closing.