Add IIIF Image API tilesource with example

src/ol/source/IIIF.js contains a tile source for IIIF Image API services.
It supports Image API version 1 and 2 on compliance levels 0, 1 and 2.

To get working constructor options for IIIF from an IIIF image info.json,
use src/ol/format/IIIFInfo.js.

An example is available in examples/iiif.html respectivly examples/iiif.js.

examples/iiif.js

@@ -0,0 +1,48 @@
+import Map from '../src/ol/Map.js';
+import View from '../src/ol/View.js';
+import TileLayer from '../src/ol/layer/Tile.js';
+import IIIF from '../src/ol/source/IIIF.js';
+import IIIFInfo from '../src/ol/format/IIIFInfo.js';
+
+const layer = new TileLayer(),
+    map = new Map({
+      layers: [layer],
+      target: 'map'
+    });
+
+const notifyDiv = document.getElementById('iiif-notification');
+
+function refreshMap(imageInfoUrl) {
+  fetch(imageInfoUrl).then(function(response) {
+    response.json().then(function(imageInfo) {
+      const options = new IIIFInfo().readFromJson(imageInfo);
+      if (options === undefined || options.version === undefined) {
+        notifyDiv.textContent = 'Data seems to be no valid IIIF image information.';
+        return;
+      }
+      const extent = [0, -options.size[1], options.size[0], 0];
+      layer.setSource(new IIIF(options));
+      map.setView(new View({
+        resolutions: layer.getSource().getTileGrid().getResolutions(),
+        extent: extent,
+        constrainOnlyCenter: true
+      }));
+      map.getView().fit(extent);
+      notifyDiv.textContent = '';
+    }).catch(function(body) {
+      notifyDiv.textContent = 'Could not read image info json. ' + body;
+    });
+  }).catch(function() {
+    notifyDiv.textContent = 'Could not read data from URL.';
+  });
+}
+
+const urlInput = document.getElementById('imageInfoUrl');
+const displayButton = document.getElementById('display');
+
+displayButton.addEventListener('click', function() {
+  const imageInfoUrl = urlInput.value;
+  refreshMap(imageInfoUrl);
+});
+
+refreshMap(urlInput.value);