Merge window operator commit to master

This is from commit http://github.com/RallySoftware/RxJava/commit/71335e4ed1531b1542c7b304a6d3337145e0b2df
Merge branch 'OperationWindow' of https://github.com/RallySoftware/RxJava

- updated to use new OnSubscribeFunc
- updated to use super/extends generics
made WINDOW_MAKER typed
removed raw Func0s from the chunks
made the public window methods more generic via the basic (lol) super/extends fluff; also simplified api by removing a few useless super definitions (there's no super of Opening and Closing)
Merge pull request #349 from benjchristensen/window-operator

Window Operator