Update Google Test to v1.10.0 (#840)

This commit updates the version of Google Test from 1.8 to 1.10.

test/gtest-1.10.0/googletest/include/gtest/internal/custom/README.md

@@ -0,0 +1,56 @@
+# Customization Points
+
+The custom directory is an injection point for custom user configurations.
+
+## Header `gtest.h`
+
+### The following macros can be defined:
+
+*   `GTEST_OS_STACK_TRACE_GETTER_` - The name of an implementation of
+    `OsStackTraceGetterInterface`.
+*   `GTEST_CUSTOM_TEMPDIR_FUNCTION_` - An override for `testing::TempDir()`. See
+    `testing::TempDir` for semantics and signature.
+
+## Header `gtest-port.h`
+
+The following macros can be defined:
+
+### Flag related macros:
+
+*   `GTEST_FLAG(flag_name)`
+*   `GTEST_USE_OWN_FLAGFILE_FLAG_` - Define to 0 when the system provides its
+    own flagfile flag parsing.
+*   `GTEST_DECLARE_bool_(name)`
+*   `GTEST_DECLARE_int32_(name)`
+*   `GTEST_DECLARE_string_(name)`
+*   `GTEST_DEFINE_bool_(name, default_val, doc)`
+*   `GTEST_DEFINE_int32_(name, default_val, doc)`
+*   `GTEST_DEFINE_string_(name, default_val, doc)`
+
+### Logging:
+
+*   `GTEST_LOG_(severity)`
+*   `GTEST_CHECK_(condition)`
+*   Functions `LogToStderr()` and `FlushInfoLog()` have to be provided too.
+
+### Threading:
+
+*   `GTEST_HAS_NOTIFICATION_` - Enabled if Notification is already provided.
+*   `GTEST_HAS_MUTEX_AND_THREAD_LOCAL_` - Enabled if `Mutex` and `ThreadLocal`
+    are already provided. Must also provide `GTEST_DECLARE_STATIC_MUTEX_(mutex)`
+    and `GTEST_DEFINE_STATIC_MUTEX_(mutex)`
+*   `GTEST_EXCLUSIVE_LOCK_REQUIRED_(locks)`
+*   `GTEST_LOCK_EXCLUDED_(locks)`
+
+### Underlying library support features
+
+*   `GTEST_HAS_CXXABI_H_`
+
+### Exporting API symbols:
+
+*   `GTEST_API_` - Specifier for exported symbols.
+
+## Header `gtest-printers.h`
+
+*   See documentation at `gtest/gtest-printers.h` for details on how to define a
+    custom printer.