Add a yolo-v3 example. (#528)

* Add a couple functions required for yolo.

* Add the yolo-v3 example.

* Add minimum and maximum.

* Use the newly introduced maximum.

* Cuda support for min/max + add some testing.

* Allow for more tests to work with accelerate.

* Fix a typo.

candle-nn/tests/loss.rs

@@ -1,3 +1,9 @@
+#[cfg(feature = "mkl")]
+extern crate intel_mkl_src;
+
+#[cfg(feature = "accelerate")]
+extern crate accelerate_src;
+
 use candle::{Device, Result, Tensor};
 mod test_utils;
 use test_utils::to_vec0_round;