Merge pull request #3895 from wp-cli/3728-package-command

Abstract `wp package *` to a separate wp-cli/package-command package

Author: schlessera

composer.json

@@ -35,7 +35,8 @@
 		"wp-cli/import-command": "^1.0",
 		"wp-cli/db-command": "^1.0",
 		"wp-cli/media-command": "^1.0",
-		"wp-cli/export-command": "^1.0"
+		"wp-cli/export-command": "^1.0",
+		"wp-cli/package-command": "^1.0"
 	},
 	"require-dev": {
 		"phpunit/phpunit": "3.7.*",