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.

src/ol/format.js

@@ -7,6 +7,7 @@ export {default as GeoJSON} from './format/GeoJSON.js';
 export {default as GML} from './format/GML.js';
 export {default as GPX} from './format/GPX.js';
 export {default as IGC} from './format/IGC.js';
+export {default as IIIFInfo} from './format/IIIFInfo.js';
 export {default as KML} from './format/KML.js';
 export {default as MVT} from './format/MVT.js';
 export {default as OWS} from './format/OWS.js';