Add some documentation and test to the linear layer. (#151)

* Add some documentation and test to the linear layer.

* Layer norm doc.

* Minor tweaks.

candle-nn/src/linear.rs

@@ -1,3 +1,22 @@
+//! Linear layer
+//!
+//! This layer applies a linear transformation to the incoming data, `y = x@w.t() + b`.
+//! The bias is optional. The `forward` method can be used to apply the layer, it supports input
+//! with a batch dimension (so of shape `(b_sz, in_c)`) or without (of shape `(in_c,)`), the
+//! output has shape `(b_sz, out_c)` and `(out_c,)` respectively.
+//!
+//! ```rust
+//! use candle::{Tensor, Device::Cpu};
+//! use candle_nn::Linear;
+//! # fn main() -> candle::Result<()> {
+//!
+//! let w = Tensor::new(&[[1f32, 2.], [3., 4.], [5., 6.]], &Cpu)?;
+//! let layer = Linear::new(w, None); // Use no bias.
+//! let xs = Tensor::new(&[[10f32, 100.]], &Cpu)?;
+//! let ys = layer.forward(&xs)?;
+//! assert_eq!(ys.to_vec2::<f32>()?, &[[210.0, 430.0, 650.0]]);
+//! # Ok(()) }
+//! ```
 use candle::Tensor;
 
 #[derive(Debug)]