Constrain the types dispatched on in Base functions like fill, ones, zeros, trues, falses

[jishnub]

Currently the function signature for fill is

OffsetArrays.jl/src/OffsetArrays.jl

Lines 212 to 213 in 7294f3d

	Base.fill(x, inds::Tuple{UnitRange,Vararg{UnitRange}}) =
	fill!(OffsetArray{typeof(x)}(undef, inds), x)

However the function clearly only works with integral values, as the OffsetArray constructor only accepts Ints. Something like this will fail:

julia> fill(3.0,UnitRange(3.0,5.0))
ERROR: MethodError: no method matching OffsetArray(::Array{Float64,1}, ::Tuple{Float64})

Should the types dispatched upon be constrained to UnitRange{<:Integer}? This will also allow other packages to define these methods for various other UnitRange types.

The same for other functions like zeros, ones, trues, falses.