Do a large chunk of the move to go

This commit moves a huge chunk of the code to go. The TODO.md document
indicates what is left to be done.

cmd/ls.go

@@ -0,0 +1,38 @@
+package cmd
+
+import (
+	wisski_distillery "github.com/FAU-CDI/wisski-distillery"
+	"github.com/FAU-CDI/wisski-distillery/env"
+)
+
+// Ls is the 'ls' command
+var Ls wisski_distillery.Command = ls{}
+
+type ls struct {
+	Positionals struct {
+		Slug []string `positional-arg-name:"SLUG" required:"0" description:"slug(s) of instance(s) to list"`
+	} `positional-args:"true"`
+}
+
+func (ls) Description() wisski_distillery.Description {
+	return wisski_distillery.Description{
+		Requirements: env.Requirements{
+			NeedsConfig: true,
+		},
+		Command:     "ls",
+		Description: "Lists WissKI instances",
+	}
+}
+
+func (l ls) Run(context wisski_distillery.Context) error {
+	instances, err := context.Environment.Instances(l.Positionals.Slug...)
+	if err != nil {
+		return err
+	}
+
+	for _, instance := range instances {
+		context.Println(instance.Slug)
+	}
+
+	return nil
+}