Structure type properties for Typed/Racket

This library allows a safer use of some struct type properties with Typed/Racket.

• Functions and values supplied to #:property prop:some-prop value-here are typechecked. Their type is computed by this library, and depends on the property.

• The API should hopefully remain stable, even if struct type properties become supported (this library will then become a wrapper) or forbidden in Typed/Racket (this library will then use typed/racket/unsafe tricks).

Currently, the following properties are supported:

• prop:custom-write
• prop:equal+hash