To make error messages from Pkl eval easier to read, this change uses
the Jansi library to colour the output, making it quicker and easier to
scan error messages and understand what's happened.
The Jansi library also detects if the CLI output is a terminal capable
of handling colours, and will automatically strip out escape codes if
the output won't support them (e.g. piping the output somewhere else).
* Add `--proxy` and `--no-proxy` CLI flags
* Add property `http` to `pkl:settings`
* Move `EvaluatorSettings` from `pkl:Project` to its own module and add property `http`
* Add support for proxying in server mode, and through Gradle
* Add `setProxy()` to `HttpClient`
* Add documentation
