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/test/native/cpp/main.cpp

@@ -5,20 +5,20 @@
 /* the project.                                                               */
 /*----------------------------------------------------------------------------*/
 
-#include "gtest/gtest.h"
+#include "gmock/gmock.h"
 
-#include "Log.h"
+#include <climits>
 
-int main(int argc, char **argv)
-{
-  nt::Logger::GetInstance().SetLogger(
-      [](unsigned int level, const char* file, unsigned int line,
-         const char* msg) {
-        std::fputs(msg, stderr);
-        std::fputc('\n', stderr);
-      });
-  nt::Logger::GetInstance().set_min_level(0);
-    ::testing::InitGoogleTest(&argc, argv);
-    int ret = RUN_ALL_TESTS();
-    return ret;
+#include "ntcore.h"
+
+int main(int argc, char** argv) {
+  nt::AddLogger(nt::GetDefaultInstance(),
+                [](const nt::LogMessage& msg) {
+                  std::fputs(msg.message.c_str(), stderr);
+                  std::fputc('\n', stderr);
+                },
+                0, UINT_MAX);
+  ::testing::InitGoogleMock(&argc, argv);
+  int ret = RUN_ALL_TESTS();
+  return ret;
 }