Hydra 0.9.4

• #22 Fixed an issue with any operator which in several occasions does not work.
• #24 Fixed never chainable if return rejected promise in recover operator closure.
• #26 Added concurrency argument in all operator; it allows you to set the number of max concurrent promises running for an all task in order to reduce memory and cpu footprint.
• #28 Fixed Promise's memory leak
• #29 Cleaned up the process of running the observer
• #18, #20 Refactoring of several func inside the Promise's class.