New: vue/html-indent rule (fixes #46)

docs/rules/html-indent.md

@@ -0,0 +1,114 @@
+# enforce consistent indentation in `<template>` (vue/html-indent)
+
+## :book: Rule Details
+
+This rule enforces a consistent indentation style in `<template>`. The default style is 4 spaces as same as [the core indent rule](http://eslint.org/docs/rules/indent).
+
+- This rule checks all tags, also all expressions in directives and mustaches.
+- In the expressions, this rule supports ECMAScript 2017 syntaxes. It ignores unknown AST nodes, but it might be confused by non-standard syntaxes.
+
+:-1: Examples of **incorrect** code for this rule:
+
+```html
+<template>
+ <div class="foo">
+   Hello.
+    </div>
+</template>
+```
+
+:+1: Examples of **correct** code for this rule:
+
+```html
+<template>
+    <div class="foo">
+        Hello.
+    </div>
+</template>
+```
+
+```html
+<template>
+    <div class="foo">
+        Hello.
+    </div>
+    <div
+        id="a"
+        class="b"
+        :other-attr="{
+            aaa: 1,
+            bbb: 2
+        }"
+        @other-attr2="
+            foo();
+            bar();
+        "
+    >
+        {{
+            displayMessage
+        }}
+    </div>
+</template>
+```
+
+## :wrench: Options
+
+```json
+{
+    "vue/html-indent": ["error", type, {
+        "attribute": 1,
+        "closeBracket": 0,
+        "ignores": []
+    }]
+}
+```
+
+- `type` (`number | "tab"`) ... The type of indentation. Default is `4`. If this is a number, it's the number of spaces for one indent. If this is `"tab"`, it uses one tab for one indent.
+- `attribute` (`integer`) ... The multiplier of indentation for attributes. Default is `1`.
+- `closeBracket` (`integer`) ... The multiplier of indentation for right brackets. Default is `0`.
+- `ignores` (`string[]`) ... The selector to ignore nodes. The AST spec is [here](https://github.com/mysticatea/vue-eslint-parser/blob/master/docs/ast.md). You can use [esquery](https://github.com/estools/esquery#readme) to select nodes. Default is an empty array.
+
+:+1: Examples of **correct** code for `{attribute: 1, closeBracket: 1}`:
+
+```html
+<template>
+    <div
+        id="a"
+        class="b"
+        other-attr=
+            "{longname: longvalue}"
+        other-attr2
+            ="{longname: longvalue}"
+        >
+        Text
+    </div>
+</template>
+```
+
+:+1: Examples of **correct** code for `{attribute: 2, closeBracket: 1}`:
+
+```html
+<template>
+    <div
+            id="a"
+            class="b"
+            other-attr=
+                "{longname: longvalue}"
+            other-attr2
+                ="{longname: longvalue}"
+        >
+        Text
+    </div>
+</template>
+```
+
+:+1: Examples of **correct** code for `{ignores: ["VAttribute"]}`:
+
+```html
+<template>
+    <div
+    id=""
+      class=""
+    />
+</template>
+```