update to yeoman-generator v0.17

Hello,
I was interested in composing this generator with another one so I thought I'd have a go at updating this to version 0.17.

The functionality is unchanged except for a new option to allow a target destination to be specified.

I added some tests for the new option, and refactored the existing ones since the arguments weren't being applied for some reason.

I tried to follow the existing style, let me know what you think.