Sketch the candle-nn crate. (#115)

* Sketch the candle-nn crate.

* Tweak the cuda dependencies.

* More cuda tweaks.

candle-nn/src/linear.rs

@@ -0,0 +1,25 @@
+use candle::Tensor;
+
+#[derive(Debug)]
+pub struct Linear {
+    weight: Tensor,
+    bias: Option<Tensor>,
+}
+
+impl Linear {
+    pub fn new(weight: Tensor, bias: Option<Tensor>) -> Self {
+        Self { weight, bias }
+    }
+
+    pub fn forward(&self, x: &Tensor) -> candle::Result<Tensor> {
+        let w = match x.dims() {
+            &[bsize, _, _] => self.weight.broadcast_left(bsize)?.t()?,
+            _ => self.weight.t()?,
+        };
+        let x = x.matmul(&w)?;
+        match &self.bias {
+            None => Ok(x),
+            Some(bias) => x.broadcast_add(bias),
+        }
+    }
+}