Add parse and format properties to po.hash().

These can be used to override the default location hash formatting e.g.
to add other parameters.  As `parse` is called every time the location
hash changes, it can be used to detect other parameters at the same
time.

polymaps.js

@@ -1763,19 +1763,27 @@ po.hash = function() {
  lat = 90 - 1e-8, // allowable latitude range
  map;
 
- function move() {
+ var parse = function(s) {
+ return s.split("/").map(Number);
+ };
+
+ var format = function(map) {
  var center = map.center(),
  zoom = map.zoom(),
- precision = Math.max(0, Math.ceil(Math.log(zoom) / Math.LN2)),
-  s1 = "#" + zoom.toFixed(2)
+ precision = Math.max(0, Math.ceil(Math.log(zoom) / Math.LN2));
+ return "#" + zoom.toFixed(2)
  + "/" + center.lat.toFixed(precision)
  + "/" + center.lon.toFixed(precision);
+ };
+
+ function move() {
+ var s1 = format(map);
  if (s0 !== s1) location.replace(s0 = s1); // don't recenter the map!
  }
 
  function hashchange() {
  if (location.hash === s0) return; // ignore spurious hashchange events
- var args = (s0 = location.hash).substring(1).split("/").map(Number);
+ var args = parse((s0 = location.hash).substring(1));
  if (args.length < 3 || args.some(isNaN)) move(); // replace bogus hash
  else {
  var size = map.size();
@@ -1799,6 +1807,18 @@ po.hash = function() {
  return hash;
  };
 
+ hash.parse = function(x) {
+ if (!arguments.length) return parse;
+ parse = x;
+ return hash;
+ }
+
+ hash.format = function(x) {
+ if (!arguments.length) return format;
+ format = x;
+ return hash;
+ }
+
  return hash;
 };
 // Default map controls.