dropTail, seekTail, splitTail

[koraa]

Functions for accessing the end of a sequence…

const dropTail = (seq, n) => chain(slidingWindow(n+1), map(first));
const seekTail = (seq, n) => chain(slidingWindow(1), last);
example splitTail([a, b, c, d, e], 2) -> [[a, b, c], [d, e]])

Add Try variants too (those are variants that won't complain if the seq is too short)…

This is symmetric with #141; the API should reflect this and both features may need to be added at the same time.