Subject based event bus (rxandroid-eventbus)

This is a long standing thing I meant to pull out of our app which has proven invaluable for us. It's just a thin wrapper around Rx subjects, but with an API that lends itself well for dependency injection.

Sample activity:
https://github.com/ReactiveX/RxAndroid/pull/60/files#diff-18

Sample service:
https://github.com/ReactiveX/RxAndroid/pull/60/files#diff-19
I would suggest checking out the implementation since it's in the public domain. It's implemented as an array rather than an actual linked list. It's more efficient than `Queue` when used like a queue, more efficient than `Stack` when used like a stack, and more efficient than `LinkedList` when used like a linked list. It's like the swiss-army knife of non-`List` collections.