add missing annotation in tutorial, typo and whitespace cleanup

[alanpost]

The mini tutorial, when introducing grammar annotation, failed to add annotate the division expression.

s/alfanumeric/alphanumeric/ along with s/alfarnumeric/alphanumeric/ in the directives documentation.

Remove whitespace between @ or @@ and the directive when discussing reserved word handling in the syntax documentation, consistent with how directives are formatted elsewhere.

[alanpost]

Reading through the documentation I found a typesetting error, a typo, and an error in the example code. I've put that all together in a single pull request but if you need this formatted differently or have other gripes about it certainly let me know.

[apalala]

Thank you, @alanpost !