Update README, change wasi primitive lib position and add some exception checks (#146)

Add exception throw when some initial checks fail in executing main or specific function

test-tools/toolchain/sysroot/include/stdlib.h

@@ -15,7 +15,7 @@ typedef unsigned int size_t;
 int atoi(const char *s);
 void exit(int status);
 long strtol(const char *nptr, char **endptr, register int base);
-unsigned long strtoul(const char *nptr, char **endptr, register int base)
+unsigned long strtoul(const char *nptr, char **endptr, register int base);
 void *malloc(size_t size);
 void *calloc(size_t n, size_t size);
 void free(void *ptr);