Full API documentation

[Caiyeon]

Since #98 made it possible to use vault token as a header, it is possible to use goldfish's functionality as rest calls, bypassing the UI.

But for this to be fully viable, goldfish's backend API specifications need a proper run-down and needs to be properly documented.

• All API should be versioned. /v1/ would be sufficient.
• Once versioned, API should NOT change easily (semantic versioning needs to be taken seriously)
• Proper documentation of each endpoint, their parameters, and expected results should be made. Perhaps using https://github.com/lord/slate