IterTools.pop should use Base.front instead of implementing it inline in a hackish way

[nsajko]

This line reimplements Base.front in a presumably suboptimal way:

IterTools.jl/src/IterTools.jl

Line 589 in 831bbd2

pop(t::NTuple) = reverse(tail(reverse(t))), t[end]

I guess this would matter for the performance of bigger tuples, that is, bigger values of k in subsets(collection, Val{k}()).

The fix is simple, just use Base.front. However, this package seems to still support Julia 1.0, and even Julia 0.7, and Base.front may have been introduced after that, because I can only find it on https://docs.julialang.org starting with Julia 1.2.