Simplify usage of the pool functions. (#662)

* Simplify usage of the pool functions.

* Small tweak.

* Attempt at using apply to simplify the convnet definition.

candle-core/src/lib.rs

@@ -91,3 +91,36 @@ extern crate intel_mkl_src;
 
 #[cfg(feature = "accelerate")]
 extern crate accelerate_src;
+
+pub trait ToUsize2 {
+    fn to_usize2(self) -> (usize, usize);
+}
+
+impl ToUsize2 for usize {
+    fn to_usize2(self) -> (usize, usize) {
+        (self, self)
+    }
+}
+
+impl ToUsize2 for (usize, usize) {
+    fn to_usize2(self) -> (usize, usize) {
+        self
+    }
+}
+
+// A simple trait defining a module with forward method using a single argument.
+pub trait Module: std::fmt::Debug {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor>;
+
+    /// Change the module to use training mode vs eval mode.
+    ///
+    /// The default implementation does nothing as this is only used for a couple modules such as
+    /// dropout or batch-normalization.
+    fn set_training(&mut self, _training: bool) {}
+}
+
+impl Module for quantized::QMatMul {
+    fn forward(&self, xs: &Tensor) -> Result<Tensor> {
+        self.forward(xs)
+    }
+}