Added two classes to convert Java Iterators and Iterables into their Ceylon equivalents
Added class to convert a list of items (any iterable) into a Java `Collection`.
Also added the counterparts for the previously added Iterator and Interable wrappers, but now to convert from the Ceylon versions to their Java equivalents.
Fixed #96 interop: add methods to get Java classes
Updated module documentation
Added documentation annotations to interop types and methods
Updated interop tests with the new methods and types