we should print NaNs, Infs in the usual way

[JeffreySarnoff]

julia> Quadmath.Float128(NaN)
nan

julia> Quadmath.Float128(Inf)
inf

it gets worse

julia> Quadmath.Float128(nan)
ERROR: UndefVarError: `nan` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
Stacktrace:
 [1] top-level scope
   @ REPL[13]:1

julia> Quadmath.Float128(inf)
ERROR: UndefVarError: `inf` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
Stacktrace:
 [1] top-level scope
   @ REPL[14]:1