Support iterable type for all() + race() + any()

[clue]

This changeset adds support for the iterable type for all() + race() + any(). Instead of only accepting an array, each function now also accepts instances implementing Traversable such as Iterator and Generator instances.

This is a pure feature addition that does not break BC. With these changes applied, our API is also pretty much identical to ES6 promises commonly used in JavaScript.

The first commit highlights how this is essentially only a new type definition and a call to iterator_to_array(). The second commit then takes advantage of a more iterative approach that uses less memory and also supports consuming infinite iterators if the resulting promise settles. The test suite confirms this has 100% code coverage.

Resolves #221
Builds on top of #149, #35, #83, #219 and others