Added eltype(itr::EachLine)

The type returned from `readlines` is `Array{Any,1}`, and the `EachLine` iterator does not specify an element type. This PR attempts to fix those two issues.

There is still an issue with the way list comprehensions are used in `collect` that makes the inferred type from `readlines` [wider than necessary](https://gist.github.com/ivarne/b447e8fccc4b9f9cf47d) (`Union(Array{String,1},Array{Union(UTF8String,ASCIIString),N})`).

Not sure if that is an issue that should be reported elsewhere.