acceptsCharsets (...args) {
    return this.accept.charsets(...args)
  }
Return accepted charsets or best fit based on `charsets`.

Given `Accept-Charset: utf-8, iso-8859-1;q=0.2, utf-7;q=0.5`
an array sorted by quality is returned:

    ['utf-8', 'utf-7', 'iso-8859-1']

@param {String|Array} charset(s)...
@return {String|Array}
@api public