Return collection of responses from send

[dwightwatson]

• send will now return a collection of MulticastSendReport instead of void. This is optional, it will still return void if there are no tokens provided.
• Not sure if there is a better object to return - but considering we do chunk results we sort of have to return the results in a batch also.
• Remove docblocks that are now covered by type hints instead.

Closes #178.

[dwightwatson]

I wonder if I should return an array instead?

[kohenkatz]

I wonder if I should return an array instead?

I believe the previous version returned an array, but I don't think that is a reason to need to return an array from this version. Collection implements the array interface, so I think older code that worked with version 3 should still work.

I have not tested this PR yet, but it looks good to me.