Updated sample code for zip.extractEntryTo. Added maintainEntryPath param.

Hey cthackers,

I updated the basic usage sample code for zip.extractEntryTo and added maintainEntryPath parameter on the README.md file. This is the change that I meant on my comment [here](https://github.com/cthackers/adm-zip/issues/54#issuecomment-21537703). I agree that your documentation is correct over [this section](https://github.com/cthackers/adm-zip/wiki/ADM-ZIP#wiki-a18). I'm only referring to the sample code on the README.md file.

Regards,

Third