Add support for registry config store

[craftbyte]

Apps that are deployed in big enterprise environments nowadays are supposed to support being configured using Group Policies. Since those are just a fancy name for Registry Settings Storage, I think it would be great if Config.Net supported a Read-Only Registry Store. A function like UseRegistry(RegistryType type, string AppName) would work. RegistryType being an enum of LocalMachine and CurrentUser, AppName being the subpath under Software in the registry.