Add layer overpass.

assets/leaflet-layer-overpass/README.md

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+Leaflet Layer OverPass
+=============================
+[![Bower version](https://badge.fury.io/bo/leaflet-layer-overpass.svg)](http://badge.fury.io/bo/leaflet-layer-overpass)
+
+## What is it?
+A [Leaflet](http://leafletjs.com/) plugin to create a custom POI overlay - thanks to the [OSM](http://www.openstreetmap.org/) dataset and the [Overpass API](http://overpass-api.de/)
+
+checkout the [demo](http://kartenkarsten.github.io/leaflet-layer-overpass/demo/)
+
+
+## Installation
+You can use bower to install leaflet-layer-overpass.
+
+Simply run
+```bash
+$ bower install --save leaflet-layer-overpass
+```
+After that you can include and use the `OverpassLayer.css` and `OverpassLayer.js` files (or `OverPassLayer.min.js` if you want the minified version) from the `dist` folder in your html.
+
+## How to use it?
+```javascript
+var attr_osm = 'Map data &copy; <a href="http://openstreetmap.org/">OpenStreetMap</a> contributors',
+attr_overpass = 'POI via <a href="http://www.overpass-api.de/">Overpass API</a>';
+var osm = new L.TileLayer('http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {opacity: 0.7, attribution: [attr_osm, attr_overpass].join(', ')});
+
+var map = new L.Map('map').addLayer(osm).setView(new L.LatLng(52.265, 10.524), 14);
+
+//OverPassAPI overlay
+var opl = new L.OverPassLayer({
+  query: "node(BBOX)['amenity'='post_box'];out;",
+});
+
+map.addLayer(opl);
+```
+In order to get a valid query the [Overpass-turbo IDE](http://overpass-turbo.eu/) might help.
+
+## What are the options?
+You can specify an options object as an argument of L.OverPassLayer.
+```javascript
+options: {
+  endpoint: "http://overpass.osm.rambler.ru/cgi/",
+  query: "node(BBOX)['amenity'='post_box'];out;",
+  debug: false,
+  callback: function(data) {
+    for(var i=0;i<data.elements.length;i++) {
+      var e = data.elements[i];
+
+      if (e.id in this.instance._ids) return;
+      this.instance._ids[e.id] = true;
+      var pos = new L.LatLng(e.lat, e.lon);
+      var popup = this.instance._poiInfo(e.tags,e.id);
+      var color = e.tags.collection_times ? 'green':'red';
+      var circle = L.circle(pos, 50, {
+        color: color,
+        fillColor: '#fa3',
+        fillOpacity: 0.5
+      })
+      .bindPopup(popup);
+      this.instance.addLayer(circle);
+    }
+  },
+  minZoomIndicatorOptions: {
+    position: 'topright',
+    minZoomMessageNoLayer: "no layer assigned",
+    minZoomMessage: "current Zoom-Level: CURRENTZOOM all data at Level: MINZOOMLEVEL"
+  }
+};
+```
+
+## Used by
+- [Gdzie](http://gdzie.bl.ee/#!7/51.495/20.995/)
+- [pois.elblogdehumitos.com.ar](http://pois.elblogdehumitos.com.ar/)
+- [briefkastenkarte.de](http://briefkastenkarte.de/)
+
+## Dependencies
+- Leaflet (tried with version 0.6.2, 0.7.3)
+
+## Development
+In order to contribute to the project you should first clone the repository. The javascript source files
+reside in the `src` folder and are concatenated and minified by gulp. If you want to make changes
+make them in the `src` folder and then build the `dist` file with gulp.
+For that you first need to install gulp if you do not have installed it yet
+```
+$ npm install --global gulp
+```
+Then install all the needed packages for this project:
+```
+$ npm install 
+```
+And then just run
+```
+gulp
+``` 
+after you made your changes. This will combine (and minify) the files and put them into the `dist` folder.
+
+
+## Further Ideas
+- OverPass result to -> geoJSON to -> Leaflet Layer to support ways and areas as well (see also [PoiMap](https://github.com/simon04/POImap/blob/master/railway.html), [OverPassTurbo](https://github.com/tyrasd/overpass-ide/blob/gh-pages/js/overpass.js))
+- improve popup text. use links, format addresses and contact details (compare with [OpenLinkMap](http://www.openlinkmap.org/))
+- improve caching - allow to store data for some days in browser
+