strict FluentComposer factories

[maiermic]

The name of FluentComposer::forArray is misleading because it does not only accept arrays but also Traversable. I would expect a type hint array for the parameter.

FluentComposer::forValue should assert that a value has been passed instead of hiding the wrong call by using no values [] (source).

Further, a non-strict version FluentComposer::forIterable or FluentComposer::forTraversable might be added.

the iterable pseudo-type [...] is an array or an object implementing Traversable see http://php.net/manual/en/function.is-iterable.php

is_iterable (introduced in PHP 7) is similar to FluentTraversable::isTraversable. Since the term Traversable is used for different types (built-in Traversable vs. FluentTraversable) FluentComposer::forIterable might be more accurate than FluentComposer::forTraversable. Actually, FluentTraversable::from accepts also FluentTraversable which is not an Iterable but that could be fixed by implementing IteratorAggregate or Iterator.