so-5.4.0: Helper methods for cooperation deregistration

There are two new methods in agent_t class: so_deregister_agent_coop() and so_deregister_agent_normally(). They allow to write more compact and readable code.

Just for a comparison:

Before v.5.4.0

void my_agent::evt_operation_fail()
{
    // Deregistering cooperation due to inability to complete operation.
    so_environment().deregister_coop(
        so_coop_name(),
        so_5::rt::dereg_reason::user_defined_reason + 100 );
}
void my_agent::evt_operation_success()
{
    // Deregistering cooperation because operation successfully completed.
    so_environment().deregister_coop(
        so_coop_name(),
        so_5::rt::dereg_reason::normal );
}

Since v.5.4.0

void my_agent::evt_operation_fail()
{
    // Deregistering cooperation due to inability to complete operation.
    so_deregister_agent_coop(
        so_5::rt::dereg_reason::user_defined_reason + 100 );
}
void my_agent::evt_operation_success()
{
    // Deregistering cooperation because operation successfully completed.
    so_deregister_agent_coop_normally();
}