Generate man-files for the config file via a proc macro

[sornas]

It's very easy to forget updating the documentation for the configuration file. A procedural macro that reads the doc comments and formats them into a man-page would ensure they stay more up-to-date. The macro would need to be recursive to handle the fact that we have an AudioConfig inside our Config and would like to document both.

• https://lib.rs/crates/man
• https://lib.rs/crates/roff
• https://lib.rs/crates/roffman