replaceFunc = function (wholeMatch, linkId, url, width, height, blankLines, title) {
    linkId = linkId.toLowerCase();
    if (url.match(/^data:.+?\/.+?;base64,/)) {
      // remove newlines
      globals.gUrls[linkId] = url.replace(/\s/g, '');
    } else {
      globals.gUrls[linkId] = showdown.subParser('encodeAmpsAndAngles')(url, options, globals);  // Link IDs are case-insensitive
    }

    if (blankLines) {
      // Oops, found blank lines, so it's not a title.
      // Put back the parenthetical statement we stole.
      return blankLines + title;

    } else {
      if (title) {
        globals.gTitles[linkId] = title.replace(/"|'/g, '&quot;');
      }
      if (options.parseImgDimensions && width && height) {
        globals.gDimensions[linkId] = {
          width:  width,
          height: height
        };
      }
    }
    // Completely remove the definition from the text
    return '';
  }
Strips link definitions from text, stores the URLs and titles in
hash references.
Link defs are in the form: ^[id]: url "optional title"