add a builtin Hammox.enumerable/1 type

[msz]

Add an enumerable type which can be parametrized by element type. This type will be checked for implementing the Enumerable protocol and then each element of the enumerable will be checked with element type.

Add a warning that this will consume the enumerable at type check time if the enumerable is lazy or has side effects.

[msz]

Don't think this makes a lot of sense anymore. That was an interesting idea but I struggle to find situations where this would be much of an improvement.