Debugging currently relies on an env var, which makes sense re: enabling debugging early on in the execution (i.e. testing the parser and things in the CLI class) but it's A) undocumented and B) not as user-friendly/obvious as a flag (which would appear in core --help).
Add a debug flag and try to find a way to tie it into the debug call, if that's doable given current structure; at the very least, document the env var.
Failing tests re #124
Implement --debug flag, fixes #124