Allow newlines when parsing recipes

[neunenak]

Addresses #1266

[casey]

Took a look at this, and I think that if this works, we should do it, even if it isn't a perfect solution. I looked at modifying the parser to switch between line-break sensitive and insensitive modes, and it seemed complicated.

[casey]

I updated this, and added a test, but I'm running into an issue where there's an indent before the parameter, and then no indent in the recipe body, which messes this up.

[laniakea64]

Given that the issue this PR aimed to resolve has been fixed and closed, is this PR still needed?

Requiring the \ continuations here is better for human-readability of justfiles. And this change would be hard to support properly in vim-just (if even possible?).

What would be the rationale for this change in current just?

[casey]

I think it's slightly nicer to not have to add \, but I agree that it's not necessary, now that there are \ line continuations, so I'll go ahead and close this.