Otto library without any Android dependency.

Hi,

The idea behind this fork is to be able to use Otto with any Java project, without depending in Android. I'm working in projects that I would like reuse all the "plain" Java code between different platforms, and even though Guava seems a nice approach, I like Otto and its concise and lightweight philosophy. 

The only special thing Android requires is Thread confinement, to distinguish between Main thread or any other thread. Since all the mechanisms still the same, I've created a new module, with that particular scenario.

I've kept all the naming and namespaces, to have the ability to update the library without breaking backwards compatibility.

I know this fork is harder to admit than any other, for those "deeper" changes, but I wanted to open the discussion with a bit of code.

Any thoughts on this?

TY.