Use stdint.h on MSVC >= 2012

Closes cesanta/mongoose#659

PUBLISHED_FROM=8a2e029715e5e7f9a2c75eea9b55270c51b273ef

mongoose.h

@@ -187,6 +187,9 @@
 #endif
 #define random() rand()
 typedef int socklen_t;
+#if _MSC_VER >= 1700
+#include <stdint.h>
+#else
 typedef signed char int8_t;
 typedef unsigned char uint8_t;
 typedef int int32_t;
@@ -195,6 +198,7 @@ typedef short int16_t;
 typedef unsigned short uint16_t;
 typedef __int64 int64_t;
 typedef unsigned __int64 uint64_t;
+#endif
 typedef SOCKET sock_t;
 typedef uint32_t in_addr_t;
 #ifndef UINT16_MAX