Modernize codebase

- Enhance CMakeLists.txt files.
- Move to Boost Test from Google Test to support pre-C++11 compilers.
- Add more configurations on CI matrix builds.
- Other minor fixes

test/fuzz_unpack_pack_fuzzer_cpp11.cpp

@@ -1,17 +1,9 @@
-#if defined(__GNUC__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wconversion"
-#endif //defined(__GNUC__)
-
-#include <gtest/gtest.h>
-
-#if defined(__GNUC__)
-#pragma GCC diagnostic pop
-#endif //defined(__GNUC__)
+#define BOOST_TEST_MODULE FUZZ_UNPACK_PACK_FUZZER
+#include <boost/test/unit_test.hpp>
 
 #include "../fuzz/unpack_pack_fuzzer.cpp"
 
-TEST(FUZZ_UNPACK_PACK_FUZZER, works)
+BOOST_AUTO_TEST_CASE(works)
 {
-  EXPECT_EQ(0, LLVMFuzzerTestOneInput(0, 0));
+  BOOST_CHECK_EQUAL(0, FuzzerTestOneInput(MSGPACK_NULLPTR, 0));
 }