Switch to Cobra

Also:
- Fixed the Makefile
- Added a Taskfile.yml (see: https://taskfile.dev)
- Updated the manual page

Signed-off-by: Shin'ya Minazuki <shinyoukai@laidback.moe>

cmd/root.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+	"git.laidback.moe/shinyoukai/mikuru"
+)
+
+var rootCmd = &cobra.Command{
+	Use: "mikuru",
+	Short: "A client for Yarn.social from the future",
+	Version: mikuru.Version,
+}
+
+func Execute() {
+	err := rootCmd.Execute()
+	if err != nil {
+		log.Fatal(err)
+	}
+}