Let the hyperbracketed ops use quasiquote..unquote-splicing delimiters

[rocketnia]

One of the more embarrassing parts of Punctaffy at the moment is the verbosity of #/^< and #/^> for hyperbrackets. Punctaffy might be more approachable if we allow the usual ` , ,@ as an additional mode for operations like list-taffy-map, taffy-quote, etc.

There are a few decisions to make about this. Do we allow these to nest with ^<d ^>d ^< ^>? What about #` #, #,@? What about quasisyntax/loc? Do we extend the notation with some kind of escape sequence notation like ,@&?

Possible answers:

Perhaps we should indeed ascribe hyperbracket notation semantics to Racket's existing notations and let most of the notations be used in conjunction with each other. This doesn't affect how Racket uses them; it only affects how Punctaffy operations traverse them. If we eventually add escape sequence taffy-notation?, then the discrepancies between Punctaffy and Racket in the treatment of these operations can be worked around.

If we're mixing and matching like this, then the only reason we should consider using ,@& as an escape sequence is if a parenthesized escape sequence isn't sufficiently readable for some reason.