added "retrieveLinks" options

Former-commit-id: a2f3bb3d3470ad9dde777f9695a94efb02ea5bf8

lib/single-file/single-file-core.js

@@ -511,6 +511,9 @@ this.singlefile.lib.core = this.singlefile.lib.core || (() => {
 			if (this.options.addProof) {
 				pageData.hash = await util.digest("SHA-256", content);
 			}
+			if (this.options.retrieveLinks) {
+				pageData.links = Array.from(new Set(Array.from(this.doc.links).map(linkElement => linkElement.href)));
+			}
 			return pageData;
 		}