GH-302, GH-421 Call agent.quit() in main thread

- this avoids the strange delay which occurs sometimes when we call it in the mach port server thread

SwiftNeoVim/NeoVimView+UiBridge.swift

@@ -181,7 +181,7 @@ extension NeoVimView {
   }
 
   public func stop() {
-    self.agent.quit()
+    self.bridgeLogger.hr()
 
     self.quitNeoVimCondition.lock()
     self.isNeoVimQuitSuccessful = true
@@ -189,7 +189,7 @@ extension NeoVimView {
     self.quitNeoVimCondition.unlock()
 
     gui.async {
-      self.bridgeLogger.mark()
+      self.agent.quit()
       self.delegate?.neoVimStopped()
     }
   }

SwiftNeoVim/NeoVimView.swift

@@ -156,7 +156,7 @@ public class NeoVimView: NSView,
   let logger = FileLogger(as: NeoVimView.self, with: URL(fileURLWithPath: "/tmp/nvv.log"))
   let bridgeLogger = FileLogger(as: NeoVimView.self,
                                 with: URL(fileURLWithPath: "/tmp/nvv-bridge.log"),
-                                shouldLogDebug: false)
+                                shouldLogDebug: nil)
   let agent: NeoVimAgent
   let grid = Grid()