Add AppVeyor CI

In addition to running unit tests on Travis, this allows executing unit tests and integration tests on the AppVeyor CI platform, against SQL Server 2008, 2012 and 2014!

You can see an example of a successful build over at https://ci.appveyor.com/project/ArthurSchreiber/tedious/build/1.0.51. Builds are currently executed against the latest versions of NodeJS 0.8, 0.10 and 0.11.

Running the integration across different SQL Server versions already helped me to tweak some of the test cases to be more error proof. This will also help to ensure that future PRs don't break tedious on one of the supported SQL Server versions.

Unfortunately, I had to disable the encrypted connection tests. I've no idea what's wrong with them, but they just hang until the connection time out kicks in.

Anyway, I'd love to see this merged ASAP.