Update Curs.php

I suggest to refactor construct like this. There is no need with the last else statement, because you already have type hinting in your consturctor. So there is no way to pass another class except DateTime
loadRates small refactoring

getStatusCode() returns integer, so there is no need to convert it into string.
Also, probably it will be more informative if user will se result code if load fails
Merge pull request #1 from RWDeV/develop

Update Curs.php