Rename catalog-zone-gen to catz across codebase

Update binary name, usage strings, generated file headers, tests,
and README. The generated BIND config header now includes the
install path: go install go.askask.com/catz@latest

main.go

@@ -14,7 +14,7 @@ func main() {
 	outputDir := flag.String("output-dir", "", "directory for output zone files (default: same as input file)")
 	bindConf := flag.String("bind-conf", "", "path to write BIND domains.conf")
 	flag.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage: catalog-zone-gen [--config path] [--output-dir path] [--bind-conf path] <input-file>\n")
+		fmt.Fprintf(os.Stderr, "Usage: catz [--config path] [--output-dir path] [--bind-conf path] <input-file>\n")
 		flag.PrintDefaults()
 	}
 	flag.Parse()