#61: modification of the Registry interface to move to full asynchronous registry mutation.
fixes #61: make listener / watcher triggering executed in an other thread than the one use to modify the registry. The threading strategy is defined by YarGuices.Builder:
 - SERIALIZED: a single thread is used to execute sequentially operation on watchers / listeners
 - PARALLEL: a cached thread pool is used to execute in parallel the operations on the watchers / listeners
fixes #61: make listener / watcher triggering executed in an other thread than the one use to modify the registry. The threading strategy is defined by YarGuices.Builder:
 - SERIALIZED: a single thread is used to execute sequentially operation on watchers / listeners
 - PARALLEL: a cached thread pool is used to execute in parallel the operations on the watchers / listeners