Support ranges (if possible)

[nsajko]

These all fail with MethodError: no method matching round(::MultiFloat{Float64, 2}, ::RoundingMode{:Down}):

map(Float64x2, 0:5)
Float64x2(0):Float64x2(5)
Float64x2(0):Float64x2(1):Float64x2(5)

The workaround is to use generators:

julia> (Float64x2(i) for i in 0:3)
Base.Generator{UnitRange{Int64}, var"#3#4"}(var"#3#4"(), 0:3)

[dzhang314]

Hey @nsajko, thanks for your interest in MultiFloats.jl and for putting this on my radar! The use of MultiFloats in ranges totally hadn't occurred to me, and this is something definitely worth supporting.

Unfortunately, it's been a while since I've had time to work on MultiFloats.jl -- grad school is occupying all my coding capacity at the moment -- but this will certainly be on the list for the next version when I get around to it.