Problems with conversions from `Rational`

[kimikage]

Normed supports the conversion to Rational, but does not support the conversion from Rational.

julia> N0f8(1//2)
ERROR: MethodError: no method matching unsafe_trunc(::Type{UInt8}, ::Rational{Int64})

---

Fixed supports the conversion from Rational, but it overflows too easily.

julia> Q0f7(1//2)
ERROR: InexactError: trunc(Int8, 128)

FixedPointNumbers.jl/src/fixed.jl

Line 15 in 7ad0f0c

Fixed{T,f}(x::Rational) where {T,f} = Fixed{T,f}(x.num)/Fixed{T,f}(x.den)