SQL Server Spatial support

**Allow conversion from native SQL Server spatial types *geometry* and *geography* to GeoJSON objects.**
Bbox are also generated.
Syntax of usage :
```cs
    IGeometryObject geoJSON = GeoJSON.Net.MsSqlSpatial.MsSqlSpatialConvert.ToGeoJSONGeometry(<nativeSqlGeometry>)
```
Uses NuGet Package "Microsoft.SqlServer.Types"