Add OSGi manifest headers

https://github.com/Netflix/RxJava/issues/154

I can't confirm that these work but submitting based on discussion on issue #154.
Subscriptions utility class and rx.subscriptions package

https://github.com/Netflix/RxJava/issues/173
0.6.0-SNAPSHOT

Bumping to 0.6.0 as about to commit some breaking changes and new packages.
Version 0.5.5
Merge pull request #181 from benjchristensen/osgi

Add OSGi manifest headers
Merge pull request #182 from benjchristensen/issue-173-subscriptions

Subscriptions utility class and rx.subscriptions package