Record improvements

Thanks for the great start on the serializers for F# types to mongo. For a little project I needed a few additional features which I thought would be useful to implement and share. The pull request contains the following stuff:

- Added NuGet package restore for the project
- Added NuGet package dependency
- Record types can be nested now without the need of an Id property
- Implemented IBsonDocumentSerializer to enable LINQ queries
- Added a missing overload on the RecordSerializer which cuased some exceptions while deserializing nested types
- Test serializing/deserializing a nested record type with as well a basic LINQ query