some checks in make release

Makefile

@@ -1,9 +1,13 @@
 VERSION = $(shell crystal eval 'require "yaml"; s = YAML.parse(File.read("./shard.yml")); puts s["version"]')
+CONST_VERSION = $(shell crystal eval 'require "./src/immutable/version"; puts Immutable::VERSION')
+GIT_STATUS = $(shell git status -s)
 
 docsite:
 	crystal docs && git checkout gh-pages && mkdir -p api && cp -r doc/. api && git add api && git commit -m "generate docs" && git push && git checkout master
 
 release:
+	@test "$(VERSION)" == "$(CONST_VERSION)" || { echo "Error: version in shards.yml does not match version in code"; exit 1; }
+	@test "$(GIT_STATUS)" == "" || { echo "Error: uncommitted changes"; exit 1; }
 	git fetch && git tag v$(VERSION) origin/master && git push origin v$(VERSION)
 	open https://github.com/lucaong/immutable/releases/new?tag=v$(VERSION)