Better implementation of WSGI String

This is a minor release which affects only synchronous usage of the Asynchronous WSGI String.

• Better support of get_version for third party packages.
• Added optional timeout HttpClient requests.
• Refactored String and renamed from AsyncString. AsyncString still available for backward compatibility.
• Added the new GreenLock class. A locking primitive for greenlets in a greenlet pool.
• Added new example to snippets directory. A simple Actor application.

First Production/Stable Release

• Python 3.4 and above only!
• No hard dependencies
• New test runner
• Dropped trollius support
• Dropped task application
• Dropped twisted integration
• Dropped data mapper application
• Dropped pulsar shell application