Precedence works in mysterious ways

[maxbrunsfeld]

Refs tree-sitter/tree-sitter-ruby#16 (comment)

1. The static conflict resolution algorithm could use some refinement. The code that checks for expected conflicts and displays the unexpected conflicts to the user actually does a better job of analyzing the conflict than the resolution algorithm.
2. Currently, since precedence only affects how tightly adjacent elements of a sequence bind to each other, precedence has no effect on singleton production like: lhs: $ => $.variable. I explicitly made it this way, but it turns out to be dumb.