add Tooltip component

add Tooltip component

components/tooltip/index.js

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+import Tooltip from './tooltip.vue';
+
+export default Tooltip;

components/tooltip/tooltip.vue

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+<template>
+    <div :class="[`${prefixCls}`]" @mouseenter="handleShowPopper" @mouseleave="handleClosePopper">
+        <div :class="[`${prefixCls}-rel`]" v-el:reference>
+            <slot></slot>
+        </div>
+        <div :class="popperClasses" transition="fade" v-el:popper v-show="!disabled && showPopper">
+            <div :class="[`${prefixCls}-content`]">
+                <div :class="[`${prefixCls}-arrow`]"></div>
+                <div :class="[`${prefixCls}-inner`]"><slot name="content">{{ content }}</slot></div>
+            </div>
+        </div>
+    </div>
+</template>
+<script>
+    import Popper from '../base/popper';
+    import { oneOf } from '../../utils/assist';
+
+    const prefixCls = 'ivu-tooltip';
+
+    export default {
+        mixins: [Popper],
+        props: {
+            placement: {
+                validator (value) {
+                    return oneOf(value, ['top', 'top-start', 'top-end', 'bottom', 'bottom-start', 'bottom-end', 'left', 'left-start', 'left-end', 'right', 'right-start', 'right-end']);
+                },
+                default: 'bottom'
+            },
+            content: {
+                type: [String, Number],
+                default: ''
+            },
+            delay: {
+                type: Number,
+                default: 0
+            },
+            disabled: {
+                type: Boolean,
+                default: false
+            }
+        },
+        data () {
+            return {
+                prefixCls: prefixCls
+            }
+        },
+        computed: {
+            popperClasses () {
+                return [
+                    `${prefixCls}-popper`,
+                    `${prefixCls}-placement-${this.placement}`
+                ]
+            }
+        },
+        methods: {
+            handleShowPopper() {
+                this.timeout = setTimeout(() => {
+                    this.showPopper = true;
+                }, this.delay);
+            },
+            handleClosePopper() {
+                clearTimeout(this.timeout);
+                this.showPopper = false;
+            }
+        }
+    }
+</script>