Add Send Location node; expand Receive's m.location output

New matrix-send-location node publishes m.location events using
matrix-js-sdk's makeLocationContent helper, so the wire format matches
Element's "Share my location". Per-message inputs are typed inputs
(msg / flow / global / num / str), defaulting to the obvious msg.*
names.

matrix-receive's m.location handler now also sets msg.latitude,
msg.longitude, msg.altitude, msg.description, msg.assetType, and
msg.timestamp on the output (additive - msg.geo_uri / msg.payload are
unchanged), so a Receive node wired straight into Send Location resends
a byte-equivalent event.

Help docs in both nodes updated.

package.json

@@ -56,7 +56,8 @@
       "matrix-get-event": "src/matrix-get-event.js",
       "matrix-event-relations": "src/matrix-event-relations.js",
       "matrix-verification": "src/matrix-verification.js",
-      "matrix-verification-action": "src/matrix-verification-action.js"
+      "matrix-verification-action": "src/matrix-verification-action.js",
+      "matrix-send-location": "src/matrix-send-location.js"
     }
   },
   "engines": {