fix undefined variable error

when optionalResults is undefined, result generate error.
modify library usage

use this as express-middlware.

ex ) app.use(fetch());
modify Readme

change content of usage
modify return value format

change foramt options.params, options.error to options.

and add error detecting method

req.checkParamErr(result object);
this method return error object when result object is error;
if result object is not error object then return false;
modify version

0.2.0 to 0.3.0
Merge branch 'release/0.3.0' into develop