Muhurat: month view for one ceremony

Comma-separated dotted paths, relative to data, to keep in the response. A path is applied to every element of an array, so planets.name means the name of each planet. Paths that match nothing come back in _fields_unmatched; a list where nothing matches at all is a 400, because an empty object would be a confident wrong answer.

Round every non-integer number in the response to this many decimal places. Integers are left alone, because an id is not a measurement. Ecliptic longitudes ship with fourteen decimals by default; 2 is about a tenth of an arcminute.

Unique per logical operation, kept across retries. For 24 hours from the first request, a repeat with the same key, method, path, body and query string returns the stored response with Idempotent-Replayed: true and costs 0 credits. The same key with a different body or query string is a 409 IDEMPOTENCY_KEY_REUSED; a repeat while the first is still running is a 409 IDEMPOTENCY_IN_PROGRESS. Only 2xx responses are kept. See /idempotency/.