Split fallback function and introduce "fallback()" and "receive()" syntax.

test/compilationTests/corion/ico.sol

@@ -275,7 +275,7 @@ contract ico is safeMath {
         require( msg.sender.send(_val) );
     }
 
-    function () external payable {
+    receive () external payable {
         /*
             Callback function. Simply calls the buy function as a beneficiary and there is no affiliate address.
             If they call the contract without any function then this process will be taken place.

test/compilationTests/corion/module.sol

@@ -140,6 +140,6 @@ contract module {
         require( msg.sender == moduleHandlerAddress );
         _;
     }
-    function() external payable {
+    receive() external payable {
     }
 }