Adapt header format to new specification

See phoboslab/qoi#37

Signed-off-by: Riccardo Binetti <[email protected]>

lib/qoix.ex

@@ -3,13 +3,12 @@ defmodule Qoix do
   Qoix is an Elixir implementation of the [Quite OK Image](https://phoboslab.org/log/2021/11/qoi-fast-lossless-image-compression) format.
   """
 
-  @header_size 12
 
   @doc """
   Returns true if the binary appears to contain a valid QOI image.
   """
-  def qoi?(<<"qoif", _width::size(16), _height::size(16), size::size(32), _::binary>> = binary)
-      when byte_size(binary) >= @header_size + size do
+  def qoi?(<<"qoif", _width::32, _height::32, channels::8, _colorspace::8, _rest::binary>>)
+      when channels == 3 or channels == 4 do
     true
   end