Leave the stream open after writing (#8)

Author: kerams

src/FsPdf/Pdf.fs

@@ -115,7 +115,7 @@ module PdfObject =
         writer.Write System.Environment.NewLine
 
     let writePdf (stream:System.IO.Stream) (pdf:PdfObject list) =
-        use writer = new System.IO.StreamWriter (stream)
+        use writer = new System.IO.StreamWriter (stream, System.Text.Encoding.UTF8, 1024, true)
         writePreamble (writer)
         let xrefs = ResizeArray<XRef>()
         pdf |> List.iter (fun p -> p |> writeSource writer xrefs; writer.WriteLine ())