Fix pattern matching

[Y-Nak]

• Fix a crash when a variable-only match branch contains multiple statements
• Avoid duplicating scrutinee evaluation in variable match branches
• Limit ormolu check to tracked source directories

[mbenke]

Maybe we should consider adding a block statement to the abstract syntax(es). I do not feel good about the Match [] [([], body)] hack.

[rodrigogribeiro]

Great! Thanks!