Rename events to past-tense (#1181)

CODE_STYLE.md

@@ -18,8 +18,21 @@ Any exception or additions specific to our project are documented below.
 
 * Parameters must be prefixed with an underscore.
 
-```
-function test(uint256 _testParameter1, uint256 _testParameter2) {
+    ```
+    function test(uint256 _testParameter1, uint256 _testParameter2) {
     ...
-}
-```
+    }
+    ```
+
+* Events should be emitted immediately after the state change that they
+  represent, and consequently they should be named in past tense.
+
+    ```
+    function _burn(address _who, uint256 _value) internal {
+      super._burn(_who, _value);
+      emit TokensBurned(_who, _value);
+    }
+    ```
+
+  Some standards (e.g. ERC20) use present tense, and in those cases the
+  standard specification prevails.