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/Handle.h

@@ -0,0 +1,65 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2016-2017. 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_HANDLE_H_
+#define NT_HANDLE_H_
+
+#include "ntcore_c.h"
+
+namespace nt {
+
+// Handle data layout:
+// Bits 30-28: Type
+// Bits 27-20: Instance index
+// Bits 19-0:  Handle index (0/unused for instance handles)
+
+class Handle {
+ public:
+  enum Type {
+    kConnectionListener = 1,
+    kConnectionListenerPoller,
+    kEntry,
+    kEntryListener,
+    kEntryListenerPoller,
+    kInstance,
+    kLogger,
+    kLoggerPoller,
+    kRpcCall,
+    kRpcCallPoller
+  };
+  enum { kIndexMax = 0xfffff };
+
+  Handle(NT_Handle handle) : m_handle(handle) {}
+  operator NT_Handle() const { return m_handle; }
+
+  NT_Handle handle() const { return m_handle; }
+
+  Handle(int inst, int index, Type type) {
+    if (inst < 0 || index < 0) {
+      m_handle = 0;
+      return;
+    }
+    m_handle = ((static_cast<int>(type) & 0xf) << 27) |
+               ((inst & 0x7f) << 20) | (index & 0xfffff);
+  }
+
+  int GetIndex() const { return static_cast<int>(m_handle) & 0xfffff; }
+  Type GetType() const {
+    return static_cast<Type>((static_cast<int>(m_handle) >> 27) & 0xf);
+  }
+  int GetInst() const { return (static_cast<int>(m_handle) >> 20) & 0x7f; }
+  bool IsType(Type type) const { return type == GetType(); }
+  int GetTypedIndex(Type type) const { return IsType(type) ? GetIndex() : -1; }
+  int GetTypedInst(Type type) const { return IsType(type) ? GetInst() : -1; }
+
+ private:
+  NT_Handle m_handle;
+};
+
+}  // namespace nt
+
+#endif  // NT_HANDLE_H_