v5.0.0 — a derived context is stated plainly, without the "~"

Every derived context loses its leading ~: "~Sidney, BC" is now "Sidney, BC". The glyph hedged every derived label identically whether the place was 2 km off or 39, which told a reader nothing they could act on. derived: true is unchanged and still says how a context was arrived at.

Breaking: a consumer sniffing context.startsWith("~") to detect a derived label must read the derived flag instead. Fixes #29 via #30. Also in this release: inlandMetres is about 9× faster on inland points (#31) and the README is split into a front door and a contributor guide (#32).