Extract prettier config from eslintrc

This is a more conventional place to store prettier config, and it means
that VSCode's prettier plugin can automatically find it.

.eslintrc.yml

@@ -1,26 +1,24 @@
 extends:
-  - "eslint:recommended"
-  - "plugin:import/typescript"
-  - "plugin:@typescript-eslint/eslint-recommended"
-  - "plugin:@typescript-eslint/recommended"
-  - "plugin:prettier/recommended"
-parser: "@typescript-eslint/parser"
+  - 'eslint:recommended'
+  - 'plugin:import/typescript'
+  - 'plugin:@typescript-eslint/eslint-recommended'
+  - 'plugin:@typescript-eslint/recommended'
+  - 'plugin:prettier/recommended'
+  - prettier
+parser: '@typescript-eslint/parser'
 parserOptions:
   project: './tsconfig.json'
 plugins:
   - import
   - node
-  - "@typescript-eslint"
+  - '@typescript-eslint'
+  - prettier
 rules:
-  prettier/prettier:
-    - error
-    - trailingComma: es5
-      singleQuote: true
-      semi: false
+  'prettier/prettier': 2
   # requires strictNullChecks compiler option, produces many errors with messages objects
-  "@typescript-eslint/strict-boolean-expressions": off
-  "@typescript-eslint/no-explicit-any": off
-  "@typescript-eslint/no-inferrable-types": off
-  "@typescript-eslint/no-empty-function": off
-  "@typescript-eslint/ban-types": off
-  "@typescript-eslint/no-unused-vars": off
+  '@typescript-eslint/strict-boolean-expressions': off
+  '@typescript-eslint/no-explicit-any': off
+  '@typescript-eslint/no-inferrable-types': off
+  '@typescript-eslint/no-empty-function': off
+  '@typescript-eslint/ban-types': off
+  '@typescript-eslint/no-unused-vars': off

.prettierrc

@@ -0,0 +1,5 @@
+{
+	"trailingComma": "es5",
+	"singleQuote": true,
+	"semi": false
+}