Add unit tests for SocketAwaitable.

Fix SocketAwaitable and SocketAwaiter classes to pass all the tests.
Add unit tests for SocketEx.

Fix SocketAwaiter class to pass all the tests.
Add a thread-safe pool for SocketAwaitables.
Add "is disposed" check to SocketAwaitable.
Add a thread-safe buffer class.
Increase assembly version to 1.0.
Update readme.
Set SocketAwaiter.IsCompleted when it completes.
Add IsCompleted check in SocketEx for fast-fail.
Add unit tests for SocketAwaiter.
Merge branch 'next' of https://github.com/safakgur/Dawn.SocketAwaitable into next