Dilated convolutions (#657)

* Add the dilation parameter.

* Restore the basic optimizer example.

* Dilation support in cudnn.

* Use the dilation parameter in the cpu backend.

* More dilation support.

* No support for dilation in transposed convolutions.

* Add dilation to a test.

* Remove a print.

* Helper function.

candle-examples/examples/yolo-v3/darknet.rs

@@ -132,6 +132,7 @@ fn conv(vb: VarBuilder, index: usize, p: usize, b: &Block) -> Result<(usize, Bl)
         stride,
         padding,
         groups: 1,
+        dilation: 1,
     };
     let conv = if bias {
         conv2d(p, filters, size, conv_cfg, vb.pp(&format!("conv_{index}")))?