Transfer replacement (#1962)

* Add Address.sendEther

* Add documentation to sendEther

* Add changelog entry

* Rename sendEther to sendValue

(cherry picked from commit 8d166f3e35)

contracts/mocks/AddressImpl.sol

@@ -10,4 +10,10 @@ contract AddressImpl {
     function toPayable(address account) external pure returns (address payable) {
         return Address.toPayable(account);
     }
+
+    function sendValue(address payable receiver, uint256 amount) external {
+        Address.sendValue(receiver, amount);
+    }
+
+    function () external payable { } // sendValue's tests require the contract to hold Ether
 }