Exclude ww=pressurised from natural waterways

fixes #47

#47

flowing_water.tagfilterfunc

@@ -3,6 +3,9 @@
 # Exclude `waterway` values which are not water.
 waterway∈dam,weir,lock_gate,sluice_gate,security_lock,fairway,dock,boatyard,fuel,riverbank,pond,check_dam,turning_point,water_point,safe_water,derelict_canal,offshore_field,boat_lift,depth_line,floating_barrier,floodgate→F;
 
+# Used for artifical pipes (cf https://github.com/amandasaurus/waterwaymap.org/issues/47)
+waterway=pressurised→F;
+
 waterway∈ditch,drain,tidal_channel→F;
 
 # Canoeists use this. This isn't water.