Build, test, publish on AppVeyor's Windows x86 for node-webkit

Additional builds targeting node-webkit on AppVeyor's x86 Windows.

They [pass the tests](https://ci.appveyor.com/project/Mapbox/node-sqlite3/build/1.0.52) on AppVeyor.

Merge this and `[publish binary]` to fix #317.

Only the node-webkit's versions [currently listed](https://github.com/rogerwang/node-webkit/blob/d4d7f14efd1e6bbb527ed45a51a1e0d5cc07249b/README.md#downloads) in the node-webkit's `README.md` (node-webkit v0.10.0 based on Node.js v0.11.13, node-webkit v0.8.6 based on Node.js v0.10.22) are targeted.