Add the mred CLI over the library, with flags accepted after positionals

issue list/show/create/update, version list/create, category
list/create, relation create. Names resolve case-insensitively against
server enumerations; -o json everywhere; exit 0/1/2 with one-line
stderr carrying the http status for API failures.

cmd/mred/main.go

@@ -0,0 +1,12 @@
+// Command mred is the Redmine CLI over the mopac-redmine-go library.
+package main
+
+import (
+	"os"
+
+	"git.knownelement.com/ukrrs/mopac-redmine-go/internal/cli"
+)
+
+func main() {
+	os.Exit(cli.Run(os.Args[1:], os.Stdout, os.Stderr))
+}