Document and/or test API via curl

It would be good to have examples of API usage via curl, either in the docs, or tests: I'd slightly prefer tests to be the priority. (Motivated by #13.)
- POST tileset
- POST tileset with preset UID
- POST tileset, invalid? (What happens if the parameters are set wrong? When is that caught?)
- GET tileset
- GET non-existent tileset
- POST viewconf
- POST viewconf with preset UID
- POST viewconf, invalid JSON, and get error
- GET viewconf
- GET non-existent viewconf