added pagination

README.md

@@ -369,6 +369,29 @@ $post = $db->post[34]; //Returns the post 34 only if it's actived.
 You can define default modifiers for all queries: not only select, but also update, delete, etc.
 
 
+### Pagination
+
+The `select` query has a special modifier to paginate the results:
+
+```php
+$posts = $db->post->select()
+    ->page(1)
+    ->limit(50)
+    ->run();
+
+//You can set the limit as second argument of page:
+$posts = $db->post->select()
+    ->page(1, 50)
+    ->run();
+
+//On paginate the results, you have three new methods in the result:
+$posts->getPage(); //1
+$posts->getPrevPage(); //NULL
+$posts->getNextPage(); //2
+```
+
+**Note:** If the result length is lower than the max limit elements per page, it's assumed that there's no more pages, so `getNextPage()` returns `NULL`.
+
 ### Fields
 
 The purpose of the `SimpleCrud\Fields` classes is to convert the data from/to the database for its usage. For example, in Mysql the format used to store datetime values is "Y-m-d H:i:s", so the class `SimpleCrud\Fields\Datetime` converts any string or `Datetime` instance to this format, and when you select this value, you get a Datetime instance. The available fields are:

src/Queries/Mysql/Select.php

@@ -23,6 +23,7 @@ class Select extends Query
     protected $orderBy = [];
     protected $statement;
     protected $mode = 2;
+    protected $page;
 
     /**
      * Change the mode to returns just the first row.
@@ -48,6 +49,28 @@ public function all()
         return $this;
     }
 
+    /**
+     * Paginate the results
+     *
+     * @param int|string $page
+     * @param int|null   $limit
+     *
+     * @return self
+     */
+    public function page($page, $limit = null) {
+        $this->page = (int) $page;
+
+        if ($this->page < 1) {
+            $this->page = 1;
+        }
+
+        if ($limit !== null) {
+            $this->limit($limit);
+        }
+
+        return $this;
+    }
+
     /**
      * {@inheritdoc}
      *
@@ -67,6 +90,24 @@ public function run()
             $result[] = $this->createRow($row);
         }
 
+        if ($this->page !== null) {
+            $current = $this->page;
+            $next = $result->count() < $this->limit ? null : $current + 1;
+            $prev = $current > 1 ? $current - 1 : null;
+
+            $result->setMethod('getPage', function () use ($current) {
+                return $current;
+            });
+
+            $result->setMethod('getNextPage', function () use ($next) {
+                return $next;
+            });
+
+            $result->setMethod('getPrevPage', function () use ($prev) {
+                return $prev;
+            });
+        }
+
         return $result;
     }
 
@@ -168,6 +209,10 @@ public function __invoke()
      */
     public function __toString()
     {
+        if ($this->page !== null) {
+            $this->offset = ($this->page * $this->limit) - $this->limit;
+        }
+
         $query = 'SELECT';
         $query .= ' '.static::buildFields($this->table->name, array_keys($this->table->fields));