Add @intlify/vue-i18n/key-format-style rule (#116)

* Add `@intlify/vue-i18n/key-format-style` rule

* Update doc and meta

Author: ota-meshi

docs/rules/README.md

@@ -16,6 +16,7 @@
 
 | Rule ID | Description |    |
 |:--------|:------------|:---|
+| [@intlify/vue-i18n/<wbr>key-format-style](./key-format-style.html) | enforce specific casing for localization keys |  |
 | [@intlify/vue-i18n/<wbr>no-duplicate-keys-in-locale](./no-duplicate-keys-in-locale.html) | disallow duplicate localization keys within the same locale |  |
 | [@intlify/vue-i18n/<wbr>no-dynamic-keys](./no-dynamic-keys.html) | disallow localization dynamic keys at localization methods |  |
 | [@intlify/vue-i18n/<wbr>no-unused-keys](./no-unused-keys.html) | disallow unused localization keys | :black_nib: |

docs/rules/key-format-style.md

@@ -0,0 +1,100 @@
+# @intlify/vue-i18n/key-format-style
+
+> enforce specific casing for localization keys
+
+This rule aims to enforces specific casing for localization key names.
+
+```yaml
+camelCaseKey: The key for this value is camel case.
+kebab-case-key: The key for this value is kebab case.
+snake_case_key: The key for this value is snake case.
+mixed_Case-key: Perhaps you don't want to use this casing.
+```
+
+## :book: Rule Details
+
+This rule reports localization keys other than the specific casing.
+Also, the following localization key definitions are reported as errors, because the casing cannot determine.
+
+:-1: Examples of **incorrect** code for this rule:
+
+```yaml
+# ✗ BAD: Use array elements.
+- message1
+- message2
+- message3
+...
+# ✗ BAD: Use object for key.
+{foo: bar}: message
+[1,2,3]: message
+```
+
+## Options
+
+```json
+{
+  "@intlify/vue-i18n/key-format-style": ["error",
+    "camelCase" | "kebab-case" | "snake_case",
+    {
+      "allowArray": false
+    }
+  ]
+}
+```
+
+- Primary Option: Select the casing you want to apply. It set to `"camelCase"` as default
+- `allowArray`: If `true`, allow the use of arrays. If `false`, disallow the use of arrays. It set to `false` as default.
+
+:+1: Examples of **correct** code for this rule with `"camelCase"`:
+
+```yaml
+# ✓ GOOD
+appTitle: I18N Management System
+```
+
+:-1: Examples of **incorrect** code for this rule with `"camelCase"`:
+
+```yaml
+# ✗ BAD
+app-title: I18N Management System
+app_title: I18N Management System
+```
+
+:+1: Examples of **correct** code for this rule with `"kebab-case"`:
+
+```yaml
+# ✓ GOOD
+app-title: I18N Management System
+```
+
+:-1: Examples of **incorrect** code for this rule with `"kebab-case"`:
+
+```yaml
+# ✗ BAD
+appTitle: I18N Management System
+app_title: I18N Management System
+```
+
+:+1: Examples of **correct** code for this rule with `"snake_case"`:
+
+```yaml
+# ✓ GOOD
+app_title: I18N Management System
+```
+
+:-1: Examples of **incorrect** code for this rule with `"snake_case"`:
+
+```yaml
+# ✗ BAD
+appTitle: I18N Management System
+app-title: I18N Management System
+```
+
+:+1: Examples of **correct** code for this rule with `{"allowArray": true}`:
+
+```yaml
+# ✓ GOOD
+- message1
+- message2
+- message3
+```

lib/rules.ts

@@ -1,4 +1,5 @@
 /** DON'T EDIT THIS FILE; was created by scripts. */
+import keyFormatStyle from './rules/key-format-style'
 import noDuplicateKeysInLocale from './rules/no-duplicate-keys-in-locale'
 import noDynamicKeys from './rules/no-dynamic-keys'
 import noHtmlMessages from './rules/no-html-messages'
@@ -8,6 +9,7 @@ import noUnusedKeys from './rules/no-unused-keys'
 import noVHtml from './rules/no-v-html'
 
 export = {
+  'key-format-style': keyFormatStyle,
   'no-duplicate-keys-in-locale': noDuplicateKeysInLocale,
   'no-dynamic-keys': noDynamicKeys,
   'no-html-messages': noHtmlMessages,