Add preliminary read support for features

src/objectliterals.jsdoc

@@ -304,6 +304,12 @@
  *     default style is the same as Google Earth.
  */
 
+/**
+ * @typedef {Object} olx.format.GMLOptions
+ * @property {string} featureNS Feature namespace.
+ * @property {string} featureType Feature type to parse.
+ */
+
 /**
  * @typedef {Object} olx.interaction.DoubleClickZoomOptions
  * @property {number|undefined} duration Animation duration in milliseconds. Default is `250`.