'zrepl version' and 'zrepl control version' subcommand + maintainer README

Version is autodetected on build using git
If it cannot be detected with git, an override must be provided.

For tracability of distros, the distroy packagers should override as
well, which is why I added a README entry for package mainatiners.

refs #35

cmd/version.go

@@ -0,0 +1,42 @@
+package cmd
+
+import (
+	"fmt"
+	"github.com/spf13/cobra"
+	"runtime"
+)
+
+var versionCmd = &cobra.Command{
+	Use:   "version",
+	Short: "print version of zrepl binary (for running daemon 'zrepl control version' command)",
+	Run:   doVersion,
+}
+
+func init() {
+	RootCmd.AddCommand(versionCmd)
+}
+
+func doVersion(cmd *cobra.Command, args []string) {
+	fmt.Println(NewZreplVersionInformation().String())
+}
+
+type ZreplVersionInformation struct {
+	Version         string
+	RuntimeGOOS     string
+	RuntimeGOARCH   string
+	RUNTIMECompiler string
+}
+
+func NewZreplVersionInformation() *ZreplVersionInformation {
+	return &ZreplVersionInformation{
+		Version:         zreplVersion,
+		RuntimeGOOS:     runtime.GOOS,
+		RuntimeGOARCH:   runtime.GOARCH,
+		RUNTIMECompiler: runtime.Compiler,
+	}
+}
+
+func (i *ZreplVersionInformation) String() string {
+	return fmt.Sprintf("zrepl version=%s GOOS=%s GOARCH=%s Compiler=%s",
+		i.Version, i.RuntimeGOOS, i.RuntimeGOARCH, i.RUNTIMECompiler)
+}