Feature: add a code formatter to the CLI

[SuperFola]

Blocked by #425

The problem

I'm frustrated when I need to format ArkScript code by hand, because (even I, the creator of the language) I don't remember every formatting rule we wrote somewhere in this organization.

Proposed solution

Integrate a code formatting option in the CLI:

# format file.ark in place
arkscript --format file.ark

# format file but do not write the changes, output them to the terminal
arkscript --format --dry-run file.ark

[SuperFola]

A pre-requisite would be to keep the comments when parsing. Currently they are discarded as they aren't useful for the codegen.

Otherwise, formatted code would be stripped of any comments.

Edit: marking this blocked by #425

[SuperFola]

A proper specification for code formatting in ArkScript will have to be drafted first and published to the website