Implement independent instances.

Previously, most of the classes were implemented as singletons so only one
instance was possible.

This change adds an instance handle-based API.  In Java, this API is located
in a different package than the old API (edu.wpi.first.networktables).

Backwards compatibility with ITable and the old NetworkTable API is largely
maintained, but a handful of classes have moved to the new package in Java
(ConnectionInfo and PersistentException), and the old JNI has been completed
replaced.

Also:
- Move SetTeam implementation to Dispatcher.
- Consistently pass time through Java and C++ Value API.
- Rename nt_Value.h to NetworkTableValue.h for consistency with Java.
- Improve documentation
- Make C++ and Java APIs more consistent
- Document RPC functions and support RPC in Java.
- Add polling features for entry and connection listeners and use them to
  move callback threads to Java level.
- Remove thread start and stop hooks (as polling is available).
- Make Notifiers, RpcServer, Dispatcher, and Storage mockable.
- Set NOTIFY_NEW on immediate entry notifications.
- Make GetTable("/") and GetTable("") equivalent.
- Generate local notification for flags update when loading persistent file.

And many unit test updates/changes:
- Use InitGoogleMock instead of InitGoogleTest in test main.
- Move test printers to TestPrinter.h/cpp.
- Provide printers for StringRef, EntryNotifier, and Handle.
- StorageTest: Check notifications.
- Add entry notifier unit tests.
- Storage: Add test for incoming entry assignment.
- Update connection listener tests.
- Add entry listener unit tests.

Fixes #11, #140, #189, #190, #192, #193, #221

src/main/native/cpp/ConnectionNotifier.cpp

@@ -0,0 +1,29 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "ConnectionNotifier.h"
+
+using namespace nt;
+
+ConnectionNotifier::ConnectionNotifier(int inst) : m_inst(inst) {}
+
+void ConnectionNotifier::Start() { DoStart(m_inst); }
+
+unsigned int ConnectionNotifier::Add(
+    std::function<void(const ConnectionNotification& event)> callback) {
+  return DoAdd(callback);
+}
+
+unsigned int ConnectionNotifier::AddPolled(unsigned int poller_uid) {
+  return DoAdd(poller_uid);
+}
+
+void ConnectionNotifier::NotifyConnection(bool connected,
+                                          const ConnectionInfo& conn_info,
+                                          unsigned int only_listener) {
+  Send(only_listener, 0, connected, conn_info);
+}