Feature: Add support for UWP builds

[BallistiX09]

I'm trying to create a Universal Windows Platform build, but I'm running onto an error where Unity is unable to load the DLL (actually the same issue I reported on Android here: https://github.com/gilzoide/unity-sqlite-net/issues/2, except this happens on both development and release builds).

I'm not sure if that's the same bug which happened on Android, or if it's because UWP isn't currently supported, but it would be ideal if UWP builds (both ARM and x86 architectures) could be supported on this plugin though.

Thanks!