Updated generatePackageXmlAndBuildXml for Windows

Windows can execute the groovy as a executable so changed the build target to use the groovy executable and pass in the script as argument.
fixed windows compatibility
Merge pull request #19 from ranad/bugfix/new

fixed windows compatibility
Closes #14 & #15
Merge branch 'bugfix/issue-14_error_running_groovy_script_windows'