`pairwise { a, b -> }` has an advantage over `w...

# stdlib

[ilya.gorbunov]

pairwise { a, b -> } has an advantage over windowed(2) { window -> } that it doesn't allocate a list to represent a window. Also being a simplified case of windowed it has an implementation more suitable to be inlined. Therefore pairwise is inline, while windowed is not.