feat: initial CLI structure

- init: create plugin boilerplate
- install: install from local path with deps
- list: show installed plugins
- validate: check manyplug.json syntax

node_modules/fs-extra/lib/json/output-json.js

@@ -0,0 +1,12 @@
+'use strict'
+
+const { stringify } = require('jsonfile/utils')
+const { outputFile } = require('../output-file')
+
+async function outputJson (file, data, options = {}) {
+  const str = stringify(data, options)
+
+  await outputFile(file, str, options)
+}
+
+module.exports = outputJson