Add a is.iterable constraint

[filipefigcorreia]

The is.collection constraint doesn't work for iterators. I suggest a is.iterable constraint is made available for such cases.

[ruimarinho]

Do you want to check if a value is iterable or iterate over its content to assert something? If the latter, I would add support for iterators on the collection() assert.

[filipefigcorreia]

Both seem useful, but the second use-case is the one that interests me the most. Adding support to the collection assert sounds reasonable 👍