IsXlsWritable: easier XlsWriter testing

WAY-59
Merge pull request #11 in WAY/way-io from WAY-59-isxlswritable-tostringxlswriterhelper to master

* commit '15450cf47dfa96391fc2977e9839f4006664bf61':
  IsXlsWritable: easier XlsWriter testing
[maven-release-plugin] prepare release way-io-1.5.2