Add dart to rust example

dart-to-rust/Makefile

@@ -0,0 +1,18 @@
+ifeq ($(shell uname),Darwin)
+    LDFLAGS := -Wl,-dead_strip
+else
+    LDFLAGS := -Wl,--gc-sections -lpthread -ldl
+endif
+
+all: target/debug/librust_add.so
+	dart src/main.dart
+
+target/debug/librust_add.so: src/lib.rs Cargo.toml
+	cargo build
+
+target/main.o: src/main.c | target
+	$(CC) -o $@ -c $<
+
+clean:
+	rm -rf target
+	rm -rf Cargo.lock