Add more classes to the Public API (#717)

* Made interfaces and classes public

* Made NamedDestinations public and fixed namespace

* Fixed NamedDestinationsProvider namespace

* Expose more internal classes as public

* Update PublicApiScannerTests

* Make setters internal

src/UglyToad.PdfPig/PdfDocument.cs

@@ -14,6 +14,7 @@
     using Tokenization.Scanner;
     using Tokens;
     using Outline;
+    using Outline.Destinations;
     using Util.JetBrains.Annotations;
 
     /// <inheritdoc />