Update count_entity_total method and README example

Author: jadsonmonteiro

README.md

@@ -263,14 +263,21 @@ print client.exists_entity(ids)
 ```
 
 ### `count_entity_total()`
-Count the number of inserted entities. This method corresponds to a [GET request at /query/count/entity/total](http://panel.slicingdice.com/docs/#api-details-api-endpoints-get-query-count-entity-total).
+Count the number of inserted entities. This method corresponds to a [POST request at /query/count/entity/total](http://panel.slicingdice.com/docs/#api-details-api-endpoints-get-query-count-entity-total).
 
 #### Request example
 
 ```python
 from pyslicer import SlicingDice
 client = SlicingDice('MASTER_OR_READ_API_KEY', uses_test_endpoint=False)
-print client.count_entity_total()
+
+tables = {
+    'tables': [
+        'default'
+    ]
+}
+
+print client.count_entity_total(tables)
 ```
 
 #### Output example

pyslicer/client.py

@@ -213,13 +213,21 @@ def count_entity(self, query):
         url = base_url + URLResources.QUERY_COUNT_ENTITY
         return self._count_query_wrapper(url, query)
 
-    def count_entity_total(self):
-        """Make a count entity total query"""
+    def count_entity_total(self, tables=None):
+        """Make a count entity total query
+
+        Keyword arguments:
+        tables -- A dictionary containing the tables in which
+                  the total query will be performed
+        """
+        if tables is None:
+            tables = {}
         base_url = self._wrapper_test()
         url = base_url + URLResources.QUERY_COUNT_ENTITY_TOTAL
         return self._make_request(
             url=url,
-            req_type="get",
+            req_type="post",
+            json_data=ujson.dumps(tables),
             key_level=0)
 
     def count_event(self, query):