Add Makefile

This includes some of the scripts I use locally to test Mio.

Makefile

@@ -0,0 +1,29 @@
+# Targets available via Rustup that are supported.
+TARGETS ?= "x86_64-apple-darwin" "x86_64-unknown-freebsd" "x86_64-unknown-linux-gnu" "x86_64-pc-windows-gnu"
+
+test:
+	cargo test --all-features
+
+# Test everythubg for the current OS/architecture and check for all targets in
+# $TARGETS.
+test_all: check_all_targets
+	cargo hack test --feature-powerset --skip guide,extra-docs,tcp,udp,uds,pipe,os-util
+	cargo hack test --feature-powerset --skip guide,extra-docs,tcp,udp,uds,pipe,os-util --release
+
+# Check all targets using all features.
+check_all_targets: $(TARGETS)
+$(TARGETS):
+	cargo hack check --target $@ --feature-powerset --skip guide,extra-docs,tcp,udp,uds,pipe,os-util
+
+install_targets:
+	rustup target add $(TARGETS)
+
+# NOTE: when using this command you might want to change the `test` target to
+# only run a subset of the tests you're actively working on.
+dev:
+	find src/ tests/ Makefile Cargo.toml | entr -d -c $(MAKE) test
+
+clean:
+	cargo clean
+
+.PHONY: test test_all check_all_targets $(TARGETS) dev clean