public HttpRequest form(final Entry<?, ?> entry, final String charset)
      throws HttpRequestException {
    return form(entry.getKey(), entry.getValue(), charset);
  }
Write the key and value in the entry as form data to the request body
<p>
The pair specified will be URL-encoded and sent with the
'application/x-www-form-urlencoded' content-type

@param entry
@param charset
@return this request
@throws HttpRequestException
lib/src/main/java/com/github/kevinsawicki/http/HttpRequest.java