Split TLS files and introduce MG_ENABLE_CUSTOM_TLS

examples/http-restful-server/Makefile

@@ -1,5 +1,6 @@
 PROG ?= example
 
+CFLAGS ?= -W -Wall -DMG_ENABLE_LINES=1
 ifneq ($(MBEDTLS_DIR),)
 CFLAGS += -DMG_ENABLE_MBEDTLS=1 -I$(MBEDTLS_DIR)/include -I/usr/include
 CFLAGS += -L$(MBEDTLS_DIR)/lib -lmbedtls -lmbedcrypto -lmbedx509
@@ -12,7 +13,7 @@ all: $(PROG)
 	$(DEBUGGER) ./$(PROG) $(ARGS)
 
 $(PROG): main.c
-	$(CC) ../../mongoose.c -I../.. -W -Wall -DMG_ENABLE_LINES=1 $(CFLAGS) -o $(PROG) main.c
+	$(CC) ../../mongoose.c -I../.. $(CFLAGS) $(EFLAGS) -o $(PROG) main.c
 
 clean:
 	rm -rf $(PROG) *.o *.dSYM *.gcov *.gcno *.gcda *.obj *.exe *.ilk *.pdb