create parent directory if it doesn't exist
Merge pull request #13 from tlancina/master

create parent directory if it doesn't exist
Android implementation change to match Cordova update of file plugin
upgraded cordova version in engines so that it is only compatible with Cordova >= 3.3.0
Cleanup PR #14: Handle null returns from mapUriToFile.
Resolve unzip() URL arguments to file locations (fixes: #15)