Avoid some duplication using a macro + add some basic example to make debugging easier.

examples/basics.rs

@@ -0,0 +1,9 @@
+use anyhow::Result;
+use candle::{Device, Tensor};
+
+fn main() -> Result<()> {
+    let x = Tensor::var(&[3f32, 1., 4.], Device::Cpu)?;
+    let y = (((&x * &x)? + &x * 5f64)? + 4f64)?;
+    println!("{:?}", y.to_vec1::<f32>()?);
+    Ok(())
+}