Resample oneway paths to produce markers.

This uses a technique created by @mbostock in http://bl.ocks.org/mbostock/4965670
Need to confirm that this is faster. It is definitely cleaner.

css/map.css

@@ -695,17 +695,14 @@ text {
     opacity: 1;
 }
 
-.oneway .textpath {
-    pointer-events: none;
-    font-size: 7px;
-    baseline-shift: 2px;
-    opacity: .7;
-}
-
 .oneway .textpath.tag-waterway {
     fill: #002F35;
 }
 
+marker#oneway-marker path {
+    fill:#000;
+}
+
 text.tag-oneway {
     fill:#91CFFF;
     stroke:#2C6B9B;