chain maps a function over a list and concatenates the results. chain
is also known as flatMap in some libraries
Dispatches to the chain method of the second argument, if present,
according to the FantasyLand Chain spec.
@func
@memberOf R
@since v0.3.0
@category List
@sig Chain m => (a -> m b) -> m a -> m b
@param {Function} fn The function to map with
@param {Array} list The list to map over
@return {Array} The result of flat-mapping list with fn
@example
var duplicate = n => [n, n];
R.chain(duplicate, [1, 2, 3]); //=> [1, 1, 2, 2, 3, 3]
R.chain(R.append, R.head)([1, 2, 3]); //=> [1, 2, 3, 1]