anyhow demo and how to handle error

[siwilizhao]

No description provided.

[chrislearn]

I have created an example: https://github.com/salvo-rs/salvo/blob/master/examples/handle_error.rs

Current implementation for anyhow is too simple, just return 500 error, we may let it more flexible in future.

If you want handle your custom error, just implement Writer trait for your custom error.

In writer function, you can access request, deport and response, so you can do something like: just show error details to internal users or in debug mode.

run command to view this example:

cargo run --example handle_error

and then view this two page in your browser:
http://localhost:7878/custom
http://localhost:7878/anyhow