Build fixes.

Former-commit-id: b90234a91ed66539ed5fba8a062987fc614af70c
Former-commit-id: d35839e652f9d25d3622e73da84503f9abd4607a
Former-commit-id: c47972b479f83e5c6cc7bbab30ca5522a355b573

src/ImageProcessor/Formats/Png/PngDecoderCore.cs

@@ -250,7 +250,7 @@ namespace ImageProcessor.Formats
             byte[] currentScanline = new byte[scanlineLength];
             int filter = 0, column = -1;
 
-            using (ZlibInputStream compressedStream = new ZlibInputStream(dataStream))
+            using (ZlibInflateStream compressedStream = new ZlibInflateStream(dataStream))
             {
                 int readByte;
                 while ((readByte = compressedStream.ReadByte()) >= 0)

src/ImageProcessor/Formats/Png/PngEncoder.cs

@@ -263,9 +263,9 @@ namespace ImageProcessor.Formats
             {
                 memoryStream = new MemoryStream();
 
-                using (ZlibOutputStream outputStream = new ZlibOutputStream(memoryStream, this.CompressionLevel))
+                using (ZlibDeflateStream deflateStream = new ZlibDeflateStream(memoryStream, this.CompressionLevel))
                 {
-                    outputStream.Write(data, 0, data.Length);
+                    deflateStream.Write(data, 0, data.Length);
                 }
 
                 bufferLength = (int)memoryStream.Length;

src/ImageProcessor/Formats/Png/PngHeader.cs

@@ -8,7 +8,7 @@ namespace ImageProcessor.Formats
     /// <summary>
     /// Represents the png header chunk.
     /// </summary>
-    internal sealed class PngHeader
+    public sealed class PngHeader
     {
         /// <summary>
         /// Gets or sets the dimension in x-direction of the image in pixels.

src/ImageProcessor/Formats/Png/Zlib/Adler32.cs

@@ -52,8 +52,8 @@ namespace ImageProcessor.Formats
     ///    checked separately. (Any sequence of zeroes has a Fletcher
     ///    checksum of zero.)"
     /// </remarks>
-    /// <see cref="ZlibInputStream"/>
-    /// <see cref="ZlibOutputStream"/>
+    /// <see cref="ZlibInflateStream"/>
+    /// <see cref="ZlibDeflateStream"/>
     internal sealed class Adler32 : IChecksum
     {
         /// <summary>