Add priority option on the server startup.

Sources/HttpServerIO.swift

@@ -17,15 +17,15 @@ public class HttpServerIO {
     private var clientSockets: Set<Socket> = []
     private let clientSocketsLock = NSLock()
     
-    public func start(listenPort: in_port_t = 8080, forceIPv4: Bool = false) throws {
+    public func start(listenPort: in_port_t = 8080, forceIPv4: Bool = false, priority: Int = DISPATCH_QUEUE_PRIORITY_BACKGROUND) throws {
         stop()
         listenSocket = try Socket.tcpSocketForListen(listenPort, forceIPv4: forceIPv4)
-        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {
+        dispatch_async(dispatch_get_global_queue(priority, 0)) {
             while let socket = try? self.listenSocket.acceptClientSocket() {
                 self.lock(self.clientSocketsLock) {
                     self.clientSockets.insert(socket)
                 }
-                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), {
+                dispatch_async(dispatch_get_global_queue(priority, 0), {
                     self.handleConnection(socket)
                     self.lock(self.clientSocketsLock) {
                         self.clientSockets.remove(socket)