update docs and renderfucntion part

Author: syshex

README.md

@@ -230,7 +230,7 @@ The `columns` array takes object of type:
     editable: Boolean,            // Optional: column cells editable? (Default: false)
     columnstyle: String         // Optional: styles to be applied to the Column Header
     cellstyle: String           // Optional: styles to be applied to the Cells of this column
-    renderfunction: Function    // Optional: Function that receives as input the entry, and returns an HTML String for drawing cell
+    renderfunction: Function    // Optional: Function that receives as input the column name and entry, and returns an HTML String for drawing cell
 }
 }
 ```
@@ -263,16 +263,16 @@ columns: [
     {
         title: "Test",
         visible: true,
-        renderfunction: renderfu
+        renderfunction: renderTestColumn
     }
 ],
 ```
 
-There must be a javascript function called `renderfu`  :
+There must be a javascript function called `renderTestColumn`  :
 
 ```javascript
 <script>
-    var renderfu = function (entry) {
+    var renderTestColumn = function (colname, entry) {
         return '<div class="btn-group" role="group" >'+
             '  <button type="button" class="btn btn-sm btn-primary"><span class="glyphicon glyphicon-ok" aria-hidden="true"></span></button>'+
             '  <button type="button" class="btn btn-sm btn-danger"><span class="glyphicon glyphicon-remove" aria-hidden="true"></span></button>'+

dist/vue-bootstrap-table.js

@@ -48,7 +48,7 @@
                     <tr v-for="entry in filteredValuesSorted " track-by="$index">
                         <td v-for="column in displayColsVisible" track-by="$index"
                             v-show="column.visible"  :class="column.cellstyle">
-                            <span v-if="column.renderfunction!==false" v-html="column.renderfunction( entry )"></span>
+                            <span v-if="column.renderfunction!==false" v-html="column.renderfunction( column.name, entry )"></span>
                             <span v-if="column.renderfunction===false && !column.editable"> {{ entry[column.name] }} </span>
                             <value-field-section v-if="column.renderfunction===false && column.editable"
                                 :entry="entry"

dist/vue-bootstrap-table.js.map

@@ -3,7 +3,7 @@ Vue.config.devtools = true;
 
 import VueBootstrapTable from './VueBootstrapTable.vue';
 
-var renderfu = function (entry) {
+var renderfu = function ( colname, entry) {
     return '<div class="btn-group" role="group" >'+
         '  <button type="button" class="btn btn-sm btn-primary"><span class="glyphicon glyphicon-ok" aria-hidden="true"></span></button>'+
         '  <button type="button" class="btn btn-sm btn-danger"><span class="glyphicon glyphicon-remove" aria-hidden="true"></span></button>'+