Merge pull request #66 from Anuken/patch-3

Workaround for gc:arc SIGSEGV in png.nim

src/pixie/fileformats/png.nim

@@ -437,9 +437,10 @@ proc encodePng*(
       raise newException(PixieError, "Invalid PNG number of channels")
 
   let data = cast[ptr UncheckedArray[uint8]](data)
+  const signature = [137.uint8, 80, 78, 71, 13, 10, 26, 10]
 
   # Add the PNG file signature
-  result.add([137.uint8, 80, 78, 71, 13, 10, 26, 10])
+  result.add(signature)
 
   # Add IHDR
   result.addUint32(13.uint32.swap())