Performs left-to-right composition of one or more Promise-returning
functions. The leftmost function may have any arity; the remaining functions
must be unary.

@func
@memberOf R
@since v0.10.0
@category Function
@sig ((a -> Promise b), (b -> Promise c), ..., (y -> Promise z)) -> (a -> Promise z)
@param {...Function} functions
@return {Function}
@see R.composeP
@example

//  followersForUser :: String -> Promise [User]
var followersForUser = R.pipeP(db.getUserById, db.getFollowers);
function pipeP() {
	  if (arguments.length === 0) {
	    throw new Error('pipeP requires at least one argument');
	  }
	  return _arity(arguments[0].length, reduce(_pipeP, arguments[0], tail(arguments)));
	}