make lazymap work with uncountable sets and rand

[zsunberg]

I would like to be able to do the following (not exactly this, but something similar):

struct Interval
    low::Float64
    high::Float64
end

Base.rand(rng::AbstractRNG, s::Random.SamplerTrivial{Interval}) = s[].low + (s[].high-s[].low)*rand(rng)

m = Lazy.lazymap(x->round(Int, x), Interval(1.0, 3.0))
rand(m)

There are two steps:

1. Create a version of lazymap for things that are not iterable (and figure out how to detect if something is iterable).
2. Create a method of rand to call through to the original object and apply the mapped function.

Is this the right package to implement it in, or is it outside the scope? (even if the uncountable set part is outside the scope, it would be nice to make rand work for finite sets)