Callee cleans the stack and first two arguments are passed in registers ecx and edx.
You could emulate this by choosing stdcall and setting the custom_registers on the arguments manually, but this is easier.
If the compiler decided to pass an argument in a register on an internal function instead of pushing it on the stack to save time, allow us to specify the register the parameter is going to be in.
DHookAddParam received another parameter to set the register.
The custom return value was lost when calling the original function.
Save and restore our own return value, if we're about to call the original function.
