Add http singleton client example

tutorials/http/singleton-client/Makefile

@@ -0,0 +1,28 @@
+PROG ?= example                   # Program we are building
+DELETE = rm -rf                   # Command to remove files
+OUT ?= -o $(PROG)                 # Compiler argument for output file
+SOURCES = main.c mongoose.c       # Source code files
+CFLAGS = -W -Wall -Wextra -g -I.  # Build options
+#CFLAGS += -fsanitize=address,undefined,alignment
+
+# Mongoose build options. See https://mongoose.ws/documentation/#build-options
+CFLAGS_MONGOOSE += -DMG_ENABLE_LINES=1
+CFLAGS_MONGOOSE += -DMG_TLS=MG_TLS_BUILTIN
+#CFLAGS_MONGOOSE += -DMG_TLS=MG_TLS_OPENSSL -L/opt/homebrew/opt/openssl/lib -I/opt/homebrew/opt/openssl/include -lssl -lcrypto
+#CFLAGS_MONGOOSE += -DMG_TLS=MG_TLS_MBED -L/opt/homebrew/opt/mbedtls/lib -I/opt/homebrew/opt/mbedtls/include -lmbedtls -lmbedcrypto -lmbedx509
+
+ifeq ($(OS),Windows_NT)   # Windows settings. Assume MinGW compiler. To use VC: make CC=cl CFLAGS=/MD OUT=/Feprog.exe
+  PROG ?= example.exe           # Use .exe suffix for the binary
+  CC = gcc                      # Use MinGW gcc compiler
+  CFLAGS += -lws2_32 -lbcrypt   # Link against Winsock library
+  DELETE = cmd /C del /Q /F /S  # Command prompt command to delete files
+endif
+
+all: $(PROG)              # Default target. Build and run program
+	$(RUN) ./$(PROG) $(ARGS)
+
+$(PROG): $(SOURCES)       # Build program from sources
+	$(CC) $(SOURCES) $(CFLAGS) $(CFLAGS_MONGOOSE) $(CFLAGS_EXTRA) $(OUT)
+
+clean:                    # Cleanup. Delete built program and all build artifacts
+	$(DELETE) $(PROG) *.o *.obj *.exe *.dSYM