fill_like default eltype should be the one of the fill value

Right now we have the signature
```
fill_like(x::AbstractArray, val, [element_type=eltype(x)], [dims=size(x)]))
```
I think it should be
```
fill_like(x::AbstractArray, val, [element_type=typeof(val)], [dims=size(x)]))
```
instead.
