[maven-release-plugin] prepare for next development iteration
RESTClient: removed 'throws IOException'.
RESTClient: putHeader() => addHeader().
HttpURLConnectionWorker: fixed User-Agent header.
HttpClientWorkers: made User-Agent optional.
RESTClient: removed multiple values for single header name feature;
construct a single header for basic auth.
CHANGES
[maven-release-plugin] prepare release 2.0.1
2.0.1 /2014-02-12/