[Document] add form components english document (#199)

* [Document] add english document of Checkbox

* [Document] add english document of Field

* [Document] add english document of NumberKeyboard

* [bugfix] NumberKeyboard should not dispaly title when title is empty

* [Document] add english document of PasswordInput

* [Document] add english document of Radio

* [document] add english document of Switch

* [bugfix] remove redundent styles in english document

* [Document] fix details

* fix Switch test cases

packages/switch/index.vue

@@ -1,5 +1,5 @@
 <template>
-  <div class="van-switch" :class="[`van-switch--${checked ? 'on' : 'off'}`, { 'van-switch--disabled': disabled }]" @click="toggleState">
+  <div class="van-switch" :class="[`van-switch--${value ? 'on' : 'off'}`, { 'van-switch--disabled': disabled }]" @click="toggleState">
     <div class="van-switch__node van-hairline-surround">
       <van-loading v-if="loading" class="van-switch__loading" />
     </div>
@@ -12,39 +12,22 @@ import Loading from '../loading';
 
 export default {
   name: 'van-switch',
+
   components: {
     [Loading.name]: Loading
   },
+
   props: {
     value: Boolean,
-    disabled: Boolean,
     loading: Boolean,
-    onChange: Function
+    disabled: Boolean
   },
-  data() {
-    return {
-      checked: this.value
-    };
-  },
-  watch: {
-    checked(val) {
-      this.$emit('input', val);
-    },
 
-    value(val) {
-      this.checked = val;
-    }
-  },
   methods: {
-    /*
-     * 开关状态交互。
-     */
-    toggleState: function() {
-      if (this.disabled || this.loading) return;
-      if (this.onChange) {
-        this.onChange(!this.checked);
-      } else {
-        this.checked = !this.checked;
+    toggleState() {
+      if (!this.disabled && !this.loading) {
+        this.$emit('input', !this.value);
+        this.$emit('change', !this.value);
       }
     }
   }