Fix warnings for unused variable in Property test :blush:
Implement #take for Stream

This method takes n as an argument and returns a Stream that will
only contain that many events from the source Stream.
Add to_array test helper and use CounterButton for more tests

The to_array helper takes a stream and sets it up to push each
occurrence to an array that it then returns. I noticed a lot of
tests were using this pattern so we could inspect the current
state of a stream so it made sense to DRY it up with a helper.
Don't keep incrementingg the length in Take once it's finished
Merge pull request #13 from seadowg/master

Add #take and to_array