feat(cli): add basis for new "emacs-builder" CLI tool written in Go

This will eventually replace the build-emacs-for-macos script that's
written in Ruby. The migration of functionality will happen bit by bit
over time.

pkg/cli/options.go

@@ -0,0 +1,49 @@
+package cli
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/hashicorp/go-hclog"
+	cli2 "github.com/urfave/cli/v2"
+)
+
+type Options struct {
+	quiet bool
+}
+
+func actionWrapper(
+	f func(*cli2.Context, *Options) error,
+) func(*cli2.Context) error {
+	return func(c *cli2.Context) error {
+		opts := &Options{
+			quiet: c.Bool("quiet"),
+		}
+
+		levelStr := c.String("log-level")
+		level := hclog.LevelFromString(levelStr)
+		if level == hclog.NoLevel {
+			return fmt.Errorf("invalid log level \"%s\"", levelStr)
+		}
+
+		// Prevent things from logging if they weren't explicitly given a
+		// logger.
+		hclog.SetDefault(hclog.NewNullLogger())
+
+		// Create custom logger.
+		logr := hclog.New(&hclog.LoggerOptions{
+			Level:      level,
+			Output:     os.Stderr,
+			Mutex:      &sync.Mutex{},
+			TimeFormat: time.RFC3339,
+			Color:      hclog.ColorOff,
+		})
+
+		ctx := hclog.WithContext(c.Context, logr)
+		c.Context = ctx
+
+		return f(c, opts)
+	}
+}