Added -Wall and -Wextra to example/Makefile

example/Makefile

@@ -1,6 +1,6 @@
 
 CC = clang++
-CFLAGS = -std=c++14 -I..
+CFLAGS = -std=c++14 -I.. -Wall -Wextra
 #OPENSSL_SUPPORT = -DCPPHTTPLIB_OPENSSL_SUPPORT -I/usr/local/opt/openssl/include -L/usr/local/opt/openssl/lib -lssl -lcrypto
 
 all: server client hello simplesvr benchmark