Switched VS build to -W4, and fixed all resulting warnings.

Change-Id: I654217cbd01a3a449503d95753e19b672ec7ec23
Tested: on Windows, Linux

samples/sample_text.cpp

@@ -24,7 +24,7 @@ using namespace MyGame::Sample;
 
 // This is an example of parsing text straight into a buffer and then
 // generating flatbuffer (JSON) text from the buffer.
-int main(int argc, const char *argv[]) {
+int main(int /*argc*/, const char * /*argv*/[]) {
   // load FlatBuffer schema (.fbs) and JSON from disk
   std::string schemafile;
   std::string jsonfile;