Added forPage function and fixed documenation

Author: nullivex

README.md

@@ -103,7 +103,7 @@ and for rendering page numbers:
 
 ```html
 <span ng-repeat="n in [] | paginationRange: pg.pages">
-	<button ng-click="pagination.toPageId(n)">{{n}}</button>
+	<button ng-click="pg.set({start: pg.forPage(n)})">{{n}}</button>
 <span>
 ```
 

angular-pagination.js

@@ -111,6 +111,17 @@ paginationModule.factory("Pagination", function(){
   pagination.prototype.last = function(){
     return Math.floor((this.pages - 1) * this.limit)
   }
+  /**
+   * Get the starting point of a specific page
+   * @param page
+   * @returns {number}
+   */
+  pagination.prototype.forPage = function(page){
+    page = parseInt(page,10) || 1
+    if(page < 1) page = 1
+    if(page > this.pages) page = this.pages
+    return (page - 1) * this.limit
+  }
   /**
    * Set the properties of the pagination
    * @param obj