Allow comparison against iterables

[jimrthy]

For issue #8: this affected both strings and arbitrary lists

[zhemao]

This seems to conflict a bit with your other pull request. Now empty vectors and empty dictionaries are no longer equivalent. Should ImmutableVector also be made to inherit from collections.Mapping?

[jimrthy]

Hmm...I wouldn't expect an empty ImmutableVector to be equal to an empty ImmutableDict, since [] != {}. I can make that work if you like (especially since it's obviously this way for a reason--I totally missed this scenario), but it seems like that would imply that ImmutableDict({0: 'a', 1: 'b', 2: 'c'}) == ImmutableVector(['a', 'b', 'c']). That almost implies they should both be == 'abc', which definitely seems wrong.

I also definitely don't think an ImmutableVector should implement containers.Mapping. That would imply that you can use things like strings for keys. That's the problem I was really trying to avoid with this: an exception from comparing a string/list against an ImmutableDict w/ the same length.

Thanks!

[zhemao]

I'll just change the unittest and merge this in then.