Typedef char16_t for older MSVC (nodejs#175)

Author: jasongin

src/node_api_types.h

@@ -4,6 +4,10 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#if !defined __cplusplus || (defined(_MSC_VER) && _MSC_VER < 1900)
+    typedef uint16_t char16_t;
+#endif
+
 // JSVM API types are all opaque pointers for ABI stability
 // typedef undefined structs instead of void* for compile time type safety
 typedef struct napi_env__ *napi_env;