* Split help message into brief and full help
Demonstrate on ansi command
Brief help is printed when running `help commands` so it doesn't clutter
the table. Full help is printed when normal help message is requested
(e.g., `help ansi`, `ansi --help`, etc.).
* Split long command descriptions
Some are not split, just edited to be shorter.
* Capitalize the usage of all commands
* Make sure every usage ends with dot
* Fix random typo
* move basic_shell_manager to nu-engine
* move basic_evaluation_context to nu-engine
* fix failing test in feature which commands/classified/external.rs
We split off the evaluation engine part of nu-cli into its own crate. This helps improve build times for nu-cli by 17% in my tests. It also helps us see a bit better what's the core engine portion vs the part specific to the interactive CLI piece.
There's more than can be done here, but I think it's a good start in the right direction.
