Change class func to static on Thread. (#101)
Change class func to static on Thread. (#101)

Motivation:
Thread is declared final, so I believe spawnAndRun should be static.

Modifications:
Change class func to static
Result:
More consistent code, and spawnAndRun is statically dispatched.
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio