Suggest using `define-syntax-parse-rule` when applicable

[jackfirth]

Many macros written in terms of define-syntax and syntax-parse can be simplified to use define-syntax-parse-rule. Resyntax should suggest rewriting these macros, as define-syntax-parse-rule macros have a lot less boilerplate and are generally much more readable. A define-syntax with syntax-parse macro that only has one clause can be rewritten, as well as define-syntax-parser macros that only have one clause. Note that references to the input syntax object as a whole can be replaced with this-syntax.

[jackfirth]

Blocked on #11.