Move common utility classes to wpiutil library. (#79)

This is a breaking change to dependencies that use the static ntcore
library.  Unless the wpiutil library is also linked, linker errors will
result.  This does not affect the shared ntcore library.

wpiutil/include/tcpsockets/NetworkAcceptor.h

@@ -0,0 +1,30 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2015. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_TCPSOCKETS_NETWORKACCEPTOR_H_
+#define WPIUTIL_TCPSOCKETS_NETWORKACCEPTOR_H_
+
+#include "tcpsockets/NetworkStream.h"
+
+namespace wpi {
+
+class NetworkAcceptor {
+ public:
+  NetworkAcceptor() = default;
+  virtual ~NetworkAcceptor() = default;
+
+  virtual int start() = 0;
+  virtual void shutdown() = 0;
+  virtual std::unique_ptr<NetworkStream> accept() = 0;
+
+  NetworkAcceptor(const NetworkAcceptor&) = delete;
+  NetworkAcceptor& operator=(const NetworkAcceptor&) = delete;
+};
+
+}  // namespace wpi
+
+#endif  // WPIUTIL_TCPSOCKETS_NETWORKACCEPTOR_H_