Change Count, Chain to produce a consistent element type

In response to @JeffBezanson's comments here: https://github.com/JuliaLang/Iterators.jl/pull/11

For Chain, it's unclear to me that this is actually a good idea.  For example, from the tests, we currently have:

```julia
julia> collect(chain(1:2:5, 0.2:0.1:1.6))
18-element Array{Float64,1}:
 1.0
 3.0
 5.0
 0.2
 0.3
 0.4
 0.5
 0.6
 0.7
 0.8
 0.9
 1.0
 1.1
 1.2
 1.3
 1.4
 1.5
 1.6
```

But, maybe the user actually wants this to produce integers for the first 3 values?  That's not clear.  Thoughts?