Add plugin types (#1527)

Covered following plugins
- addAttributesToSVGElement.js 
- addClassesToSVGElement.js 
- cleanupAttrs.js 
- convertEllipseToCircle.js 
- removeAttributesBySelector.js 
- removeAttrs.js 
- removeComments.js 
- removeDesc.js 
- removeDoctype.js 
- removeElementsByAttr.js 
- removeEmptyText.js 
- removeMetadata.js 
- removeRasterImages.js 
- removeScriptElement.js 
- removeStyleElement.js 
- removeTitle.js 
- removeXMLProcInst.js

plugins/removeRasterImages.js

@@ -13,6 +13,8 @@ exports.description = 'removes raster images (disabled by default)';
  * @see https://bugs.webkit.org/show_bug.cgi?id=63548
  *
  * @author Kir Belevich
+ *
+ * @type {import('../lib/types').Plugin<void>}
  */
 exports.fn = () => {
   return {