code: public OkRequest<T> form(final String name, final String value) {
          return form(name, value, CHARSET_UTF8);
      }
docs: Write the name/value pair as form data to the request body
  <p/>
  The pair specified will be URL-encoded in UTF-8 and sent with the
  'application/x-www-form-urlencoded' content-type
  
  @param name
  @param value
  @return this request