fix #63 (part1 - cell editing validation)

* implement cell editing validation

* add test cases for cell editing validation

* add story for validator for cell editor

* add docs for cell editor validation

docs/README.md

@@ -42,6 +42,7 @@ Following is a `cellEdit` object:
 {
   mode: 'click',
   blurToSave: true,
+  timeToCloseMessage: 2500,
   onEditing: (rowId, dataField, newValue) => { ... },
   beforeSaveCell: (oldValue, newValue, row, column) => { ... },
   afterSaveCell: (oldValue, newValue, row, column) => { ... },
@@ -49,10 +50,13 @@ Following is a `cellEdit` object:
 }
 ```
 #### <a name='cellEdit.mode'>cellEdit.mode - [String]</a>
-`cellEdit.mode` possible value is `click` and `dbclick`. It's required value that tell `react-bootstrap-table2` how to trigger the cell editing.
+`cellEdit.mode` possible value is `click` and `dbclick`. **It's required value** that tell `react-bootstrap-table2` how to trigger the cell editing.
 
 #### <a name='cellEdit.blurToSave'>cellEdit.blurToSave - [Bool]</a>
 Default is `false`, enable it will be able to save the cell automatically when blur from the cell editor.
 
 #### <a name='cellEdit.nonEditableRows'>cellEdit.nonEditableRows - [Function]</a>
 `cellEdit.nonEditableRows` accept a callback function and expect return an array which used to restrict all the columns of some rows as non-editable. So the each item in return array should be rowkey(`keyField`)
+
+#### <a name='cellEdit.timeToCloseMessage'>cellEdit.timeToCloseMessage - [Function]</a>
+If a [`column.validator`](./columns.md#validator) defined and the new value is invalid, `react-bootstrap-table2` will popup a alert at the bottom of editor. `cellEdit.timeToCloseMessage` is a chance to let you decide how long the alert should be stay. Default is 3000 millisecond.

docs/columns.md

@@ -26,6 +26,7 @@ Available properties in a column object:
 * [headerAlign](#headerAlign)
 * [headerAttrs](#headerAttrs)
 * [editable](#editable)
+* [validator](#validator)
 
 Following is a most simplest and basic usage:
 
@@ -417,4 +418,25 @@ A new `Object` will be the result of element headerAttrs.
 > overwrited when other props related to HTML attributes were given.
 
 ## <a name='editable'>column.editable - [Bool]</a>
-`column.editable` default is true, means every column is editable if you configure [`cellEdit`](./README.md#cellEdit). But you can disable some columns editable via setting `false`.
+`column.editable` default is true, means every column is editable if you configure [`cellEdit`](./README.md#cellEdit). But you can disable some columns editable via setting `false`.
+
+## <a name='validator'>column.validator - [Function]</a>
+`column.validator` used for validate the data when cell on updating. it's should accept a callback function with following argument:
+`newValue`, `row` and `column`:
+
+```js
+{
+  // omit...
+  validator: (newValue, row, column) => {
+    return ...;
+  }
+}
+```
+
+The return value can be a bool or an object. If your valiation is pass, return `true` explicitly. If your valiation is invalid, return following object instead:
+```js
+{
+  valid: false,
+  message: 'SOME_REASON_HERE'
+}
+```