QueryFilter has no NEAR (location within distance) filter #490

openapi.yaml lists NEAR as a comparator, but QueryFilter (Sources/MistKit/Models/Queries/QueryFilter.swift) has no factory for it. The Filter schema also has no distance field, so a "location within N metres" query can't be sent.

Proposal: add distance to Filter (check it against the Web Services request shape) and QueryFilter.near(_:_:radiusInMeters:). Also check whether QuerySort is missing relativeLocation.

Found while building brightdigit/Mistico (vendored at Packages/MistKit, branch mistico from v1.0.0-beta.6). Tracked in brightdigit/Mistico#106.