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.html

@@ -0,0 +1,16 @@
+---
+layout: example.html
+title: IIIF Image API
+shortdesc: Example of a IIIF Image API source.
+docs: >
+  Example of a tile source for an International Image Interoperability Framework (IIIF) Image Service.
+  Try any Image API version 1 or 2 service.
+tags: "IIIF, IIIF Image API, tile source"
+---
+<div id="map" class="map"></div>
+<div class="controls">
+  <div id="iiif-notification">&nbsp;</div>
+  Enter <code>info.json</code> URL:
+  <input type="text" id="imageInfoUrl" value="https://iiif.ub.uni-leipzig.de/iiif/j2k/0000/0102/0000010218/00000061.jpx/info.json">
+  <button id="display">Display image</button>
+</div>