Add publishing to appveyor

[springmeyer]

Before tagging a new release (#38) (the first with windows support) we'll need to add node-pre-gyp publishing to the appveyor config.

[springmeyer]

@BergWerkGIS - could you lead this out? @joto and I just spoke about moving more logic for travis to separate scripts like this. What do you think about doing that for appveyor scripts? That way we could better re-use those scripts between repos.

[springmeyer]

closing per #76 (comment)