Add semver (#595)

Add a version.go that has the semver version of this libary; now at
1.0.0. Use a struct so external code can easily check the for the
version without resulting to string parsing. Add String() function if
you want to access the version string.

Use simple Makefile.release to kick off a new release:

% edit version.go
% make -f Makefile.release

will tag and push according to version, if version is 1.0.0 the tag
in git will be v1.0.0

Makefile.release

@@ -0,0 +1,51 @@
+# Makefile for releasing.
+#
+# The release is controlled from version.go. The version found there is
+# used to tag the git repo, we're not building any artifects so there is nothing
+# to upload to github.
+#
+# * Up the version in version.go
+# * Run: make -f Makefile.release release
+#   * will *commit* your change with 'Release $VERSION'
+#   * push to github
+#
+
+define GO
+//+build ignore
+
+package main
+
+import (
+	"fmt"
+
+	"github.com/miekg/dns"
+)
+
+func main() {
+	fmt.Println(dns.Version.String())
+}
+endef
+
+$(file > version_release.go,$(GO))
+VERSION:=$(shell go run version_release.go)
+TAG="v$(VERSION)"
+
+all:
+	@echo Use the \'release\' target to start a release $(VERSION)
+	rm -f version_release.go
+
+.PHONY: release
+release: commit push
+	@echo Released $(VERSION)
+	rm -f version_release.go
+
+.PHONY: commit
+commit:
+	@echo Committing release $(VERSION)
+	git commit -am"Release $(VERSION)"
+	git tag $(TAG)
+
+.PHONY: push
+push:
+	@echo Pushing release $(VERSION) to master
+	git push --tags

version.go

@@ -0,0 +1,15 @@
+package dns
+
+import "fmt"
+
+// Version is current version of this library.
+var Version = V{1, 0, 0}
+
+// V holds the version of this library.
+type V struct {
+	Major, Minor, Patch int
+}
+
+func (v V) String() string {
+	return fmt.Sprintf("%d.%d.%d", v.Major, v.Minor, v.Patch)
+}

version_test.go

@@ -0,0 +1,10 @@
+package dns
+
+import "testing"
+
+func TestVersion(t *testing.T) {
+	v := V{1, 0, 0}
+	if x := v.String(); x != "1.0.0" {
+		t.Fatalf("Failed to convert version %v, got: %s", v, x)
+	}
+}