Revisit nested quasiquotes

[Mercerenies]

#40 defined nested quasiquote semantics. Revisit this, I find them very unintuitive.

``,,x

evaluates to

`,1

if x has value 1. How often do we want a nested quasiquote to evaluate to another unquote form? In my mind, a double unquote should eat both unquotes in a nested quasiquote.