Make <?> infixr and update prec to 2

[JordanMartinez]

Description of the change

Fixes #161

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Checklist:

• Added the change to the changelog's "Unreleased" section with a link to this PR and your username
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation in the README and/or documentation directory
• Added a test for the contribution (if applicable)

[JordanMartinez]

🏓 @thomashoneyman

[JordanMartinez]

I don't think setting <?> to 2 actually works.

[thomashoneyman]

Wait, sorry — I was about to say the same thing 😓. This isn't exercised in tests at all in this library. We need to add it there. Sorry about that, I just assumed it was already used there and would have thrown.

[JordanMartinez]

No worries! I'll submit another PR.

[natefaubion]

I actually think that this should be 3, on second thought. It having the same precedence as alt means that you can just write things like:

foo <?> "ok"
  <|> bar <?> "wat

Even if a formatter will mess it up.