GML parser.

This adds a parser (read/write) for GML v2 and v3. GML v3 is limited to the
simple features profile of GML 3.1.1, just like OpenLayers 2 was. This will
be the basis for the WFS parser, but it only makes sense to continue this work
once feature modification (insert, update, delete) is in place in ol3. So the
WFS parser will be another pull request.

examples/gml.js

@@ -0,0 +1,61 @@
+goog.require('ol.Collection');
+goog.require('ol.Map');
+goog.require('ol.RendererHint');
+goog.require('ol.View2D');
+goog.require('ol.layer.TileLayer');
+goog.require('ol.layer.Vector');
+goog.require('ol.parser.ogc.GML_v3');
+goog.require('ol.projection');
+goog.require('ol.source.MapQuestOpenAerial');
+goog.require('ol.source.Vector');
+goog.require('ol.style.Polygon');
+goog.require('ol.style.Rule');
+goog.require('ol.style.Style');
+
+var raster = new ol.layer.TileLayer({
+  source: new ol.source.MapQuestOpenAerial()
+});
+
+var vector = new ol.layer.Vector({
+  source: new ol.source.Vector({
+    projection: ol.projection.get('EPSG:4326')
+  }),
+  style: new ol.style.Style({rules: [
+    new ol.style.Rule({
+      symbolizers: [
+        new ol.style.Polygon({
+          strokeColor: '#bada55'
+        })
+      ]
+    })
+  ]})
+});
+
+var map = new ol.Map({
+  layers: new ol.Collection([raster, vector]),
+  renderer: ol.RendererHint.CANVAS,
+  target: 'map',
+  view: new ol.View2D({
+    center: [-10997171.194994785, 5206335.565590534],
+    zoom: 4
+  })
+});
+
+var gml = new ol.parser.ogc.GML_v3({xy: false});
+
+var url = 'data/gml/topp-states-wfs.xml';
+var xhr = new XMLHttpRequest();
+xhr.open('GET', url, true);
+
+
+/**
+ * onload handler for the XHR request.
+ */
+xhr.onload = function() {
+  if (xhr.status == 200) {
+    // this is silly to have to tell the layer the destination projection
+    var projection = map.getView().getProjection();
+    vector.parseFeatures(xhr.responseText, gml, projection);
+  }
+};
+xhr.send();