tweak code formatting rules

* output as "json-stringify" (which is most similar to most files currently in the repository)
* add .editorconfig
* drop (now) superfluous pretter settings
* add npm commands to check code style

.prettierrc

@@ -1,8 +1,5 @@
 {
-	"tabWidth": 4,
-	"useTabs": false,
-	"semi": false,
-	"printWidth": 80,
+	"parser": "json-stringify",
 	"proseWrap": "never",
 	"bracketSpacing": true,
 	"endOfLine": "lf"