Analog of `diff` operator for adjacent sum

[stevengj]

@jling

function adjsum(ary)
           ary1 = @view ary[begin:end-1]
           ary2 = @view ary[begin+1:end]
           ary1 + ary2
       end

More compact to write:

@views adjsum(a) = a[begin:end-1] + a[begin+1:end]

Using the @views macro you can opt-in to views for slices for a whole function at once.