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/IStorage.h

@@ -0,0 +1,64 @@
+/*----------------------------------------------------------------------------*/
+/* 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 NT_ISTORAGE_H_
+#define NT_ISTORAGE_H_
+
+#include <functional>
+#include <memory>
+#include <vector>
+
+#include "llvm/ArrayRef.h"
+#include "llvm/StringRef.h"
+
+#include "Message.h"
+#include "ntcore_cpp.h"
+
+namespace nt {
+
+class IDispatcher;
+class NetworkConnection;
+
+class IStorage {
+ public:
+  IStorage() = default;
+  IStorage(const IStorage&) = delete;
+  IStorage& operator=(const IStorage&) = delete;
+  virtual ~IStorage() = default;
+
+  // Accessors required by Dispatcher.  An interface is used for
+  // generation of outgoing messages to break a dependency loop between
+  // Storage and Dispatcher.
+  virtual void SetDispatcher(IDispatcher* dispatcher, bool server) = 0;
+  virtual void ClearDispatcher() = 0;
+
+  // Required for wire protocol 2.0 to get the entry type of an entry when
+  // receiving entry updates (because the length/type is not provided in the
+  // message itself).  Not used in wire protocol 3.0.
+  virtual NT_Type GetMessageEntryType(unsigned int id) const = 0;
+
+  virtual void ProcessIncoming(std::shared_ptr<Message> msg,
+                               NetworkConnection* conn,
+                               std::weak_ptr<NetworkConnection> conn_weak) = 0;
+  virtual void GetInitialAssignments(
+      NetworkConnection& conn, std::vector<std::shared_ptr<Message>>* msgs) = 0;
+  virtual void ApplyInitialAssignments(
+      NetworkConnection& conn, llvm::ArrayRef<std::shared_ptr<Message>> msgs,
+      bool new_server, std::vector<std::shared_ptr<Message>>* out_msgs) = 0;
+
+  // Filename-based save/load functions.  Used both by periodic saves and
+  // accessible directly via the user API.
+  virtual const char* SavePersistent(StringRef filename,
+                                     bool periodic) const = 0;
+  virtual const char* LoadPersistent(
+      StringRef filename,
+      std::function<void(std::size_t line, const char* msg)> warn) = 0;
+};
+
+}  // namespace nt
+
+#endif  // NT_ISTORAGE_H_