Distinguish ~(deref a) from ~@a, don't unexpand reader macros if lossy

[frenchy64]

There are several problems unexpanding reader macros, sometimes yielding pretty-printings that don't round-trip.

1. ~(deref foo) and ~ @foo are being printed as ~@foo.
2. reader macros are being unexpanded even with the wrong number of arguments
   • (var) => (var nil)
   • (var 1 2 3) => (var 1)
3. The op of a reader expansion is not being checked thoroughly enough.
   • (let [deref a] (deref a)) => (let [deref a] @a)

I try and fix all these issues in this PR.