Cleanup and overhaul (#21)

* Syntax cleanup

* More minor cleanup, use Linq

* Fix broken features by using correct values

* Feature flags the same

* Features are modular

* No AlphaFS, more .NET versions

* Fix appveyor

* Put back identifiers, for some reason

* String interpolation, modernization

* Better use of GetField

* XmlTextWriter to remove possible issues

* Fix header for OpenMSX

SabreTools.Library/DatFiles/DatHeader.cs

@@ -1,4 +1,5 @@
 using System;
+
 using SabreTools.Library.Data;
 
 namespace SabreTools.Library.DatFiles