XML docs; code cleanup (tabs->spaces; String->string)

Hi,

We are trying to use Thrift in one of our projects but we ran into some very fundamental issues:

• The "csharp" project does not target ".NET Standard" and there's only a very old release on nuget.org ( if https://www.nuget.org/packages/Thrift/ is the official one).
• The "netcore" project does target ".NET Standard" but there's no release yet ( https://issues.apache.org/jira/browse/THRIFT-4512 ) and it also has a dependency on ASP.NET Core ( https://issues.apache.org/jira/browse/THRIFT-4534 ) which makes it unusable in non-web projects.

I'm wondering why there even are 2 separate projects for .NET? It's important to understand that ".NET Core" is not a new programming API - It's just a new platform - very similar to Silverlight, Mono, Windows Phone. This means that it would also be possible to support .NET Core and the new ".NET Standard" (which represents a common set of APIs for all platforms) with the existing "csharp" project. 

Was this a deliberate decision - e.g. to make the "netcore" code the official successor of the "csharp" code? 

Would you be interested in merging the code back into one library? I'd be willing to help if you want!

It would be great to get one proper, up to date and official .NET library soon as there's already quite a lot of weird forks on NuGet.org: https://www.nuget.org/packages?q=Thrift