Better logging design

[Veetaha]

Current design of logging doesn't look well.
We have echo_cli and echo_err switches on devx_cmd::Cmd and our devx_pre_commit crate enables or disables them unsystematically making some heuristic assumptions that should actually be made by the users of the crate instead.

I suppose it is better to use log crate for logging so that the user of devx can pick the implementation of the logger it wants and filter the necessary logs.
The prefect logging implementation for xtask uses would be simplelog, however I don't like that it uses println!() and not eprintln!(). It might be reasonable to add a feature to select logging to stderr in this crate (Drakulix/simplelog.rs#62)