write an nmea trace to a unix socket for indoor maps testing

while : ; do fennel fake-nmea.fnl foo.nmea ./fake-nmea.sock ; done

pkgs/maps/fake-nmea.fnl

@@ -0,0 +1,10 @@
+(local { : sleep } (require :posix.unistd))
+
+(let [[filename socketname]  arg
+      socket (io.popen (.. "socat - unix-listen:" socketname) :w)]
+  (with-open [handle (io.open filename :r)]
+    (each [l (handle:lines "L")]
+      (if (string.match l "GNS") (sleep 1))
+      (socket:write l)
+      (socket:flush)
+      )))