Add support for watch

[No9]

Now there is support for test libraries https://github.com/No9/roche/tree/main/examples/full
It would be nice to include a watcher that monitors the project folder and does an auto build-test.
This may be possible with a shell using the stat command but it may be a feature that is implemented with the port to native code.

[No9]

Looking at mdbook implementation https://github.com/rust-lang/mdBook/blob/master/src/cmd/watch.rs#L109
A watch should be put on the src folder and the test code executed.