separated list of html elements
      in lowercase.

      validTags: ["div", "form"]

      The above example would enable curvyCorners on FORM elements.
      */
      settings = {
          tl: { radius: 20 },
          tr: { radius: 20 },
          bl: { radius: 20 },
          br: { radius: 20 },
          antiAlias: true,
          autoPad: true,
          validTags: ["div"]
      }

      /*
      Usage:

      newCornersObj = new curvyCorners(settingsObj, classNameStr);
      newCornersObj = new cur