make tokenizer classes internal and change the file header to use a scanner rather than the pdfbox type reader

src/UglyToad.Pdf/Tokenization/Scanner/ITokenScanner.cs

@@ -2,7 +2,7 @@
 {
     using Tokens;
 
-    public interface ITokenScanner
+    internal interface ITokenScanner
     {
         bool MoveNext();
 
@@ -10,4 +10,11 @@
 
         bool TryReadToken<T>(out T token) where T : class, IToken;
     }
+
+    internal interface ISeekableTokenScanner : ITokenScanner
+    {
+        void Seek(long position);
+
+        long CurrentPosition { get; }
+    }
 }