Fixes leak and Socket.disconnect() not calling onClose (davidstump#112)

* Fix Socket.disconnect not calling onClose

Since connection.delegate is nil'd out, the Socket wasn't getting the
`websocketDidDisconnect(socket:error:)` delegate message so it'd never
call onClose callbacks.

This also fixes an issue where the Socket would never be deinit'd
because the current run loop had a strong reference to it (via the
heartbeatTimer)

* Stop timer & fire onClose directly

instead of relying on the `onConnectionClosed()` function.
`onConnectionClosed()` does some additional things that we don't want
(i.e. starting the reconnect timer) to happen when a Socket is
explicitly disconnected.

* Add tests for disconnect() calling onClose

Sources/Socket.swift

@@ -186,6 +186,9 @@ public class Socket {
     public func disconnect(_ callback: (() -> Void)? = nil) {
         connection.delegate = nil
         connection.disconnect()
+
+        self.heartbeatTimer?.invalidate()
+        self.onCloseCallbacks.forEach( { $0() } )
 
         callback?()
     }

Tests/SocketSpec.swift

@@ -104,6 +104,18 @@ class SocketSpec: QuickSpec {
                 expect(fakeConnection.delegate).to(beNil())
                 expect(callbackCalled).to(beTrue())
             })
+
+            it("should fire onClose", closure: {
+                var onCloseCallsCount = 0
+                var onCloseCalled: Bool { return onCloseCallsCount > 0 }
+
+                socket.onClose(callback: {
+                    onCloseCallsCount += 1
+                })
+                socket.disconnect()
+
+                expect(onCloseCalled).to(beTrue())
+            })
         }
 
         describe(".connect()") {