chore: rename keystone to draft

Rename the module, CLI command name, and all references from
keystone/basalt to draft, and fix the stale build/README content
found along the way.

cmd/key.go

@@ -16,7 +16,7 @@ var defaultSize = 32
 var keyCmd = &cobra.Command{
 	Use:   "key [size]",
 	Short: "Generate a new cryptographic key",
-	Long:  `Generate a new cryptographic key for use in Keystone projects.`,
+	Long:  `Generate a new cryptographic key for use in Draft projects.`,
 	Run: func(cmd *cobra.Command, args []string) {
 		var keyLength int
 		if cmd.Flags().Lookup("size").Changed {