Make a complete example with a simple language

[fflorent]

It could be really helpful to implement a full example using a simple language like JSON or toml.

https://github.com/Geal/nom/blob/master/examples/json.rs

Originally suggested by @Geal.

[bikeshedder]

I'm using nom + nom_locate in the webwire CLI tool for parsing the IDL:

Language spec: https://webwire.dev/idl.html
Parser implementation: https://github.com/webwire/webwire-cli/tree/master/src/idl

I consider this to be a rather simple language and the code contains testcases including checks that the parser errors report the correct line and column numbers.