so-5.5.1: New send function family

The traditional way of sending messages and signals have two small drawbacks.

1. There is some level of verbosity in preparing and sending messages:

// In C++11, where there is no std::make_unique from C++14.
auto msg = std::unique_ptr< my_message >( new my_message( some_args ) );
mbox->deliver_message( std::move( msg ) );

Especially when sending a delayed messages:

auto msg = std::unique_ptr< my_message >( new my_message( some_args ) );
so_environment().single_timer( std::move( msg ), mbox, pause );

1. There is a difference in sending messages and signals:

// Message sending.
mbox->deliver_message( msg );
 
// Signal sending.
mbox->deliver_signal< my_signal >();

This makes template-based programming a little bit difficult.

To simplify SObjectizer usage and reduce verbosity of the code a new family of so_5::send functions is introduced.

The simple message sending can be written as:

so_5::send< my_message >( mbox, some_args );

It is an equivalent of:

auto msg = std::unique< my_message >( new my_message( some_args ) );
mbox->deliver_message( std::move( msg ) );

By utilizing variadic templates of C++11 the some_args can me a sequence of arguments:

so_5::send< msg_connect >( mbox, ip_address, ip_port, waiting_time );

The same form of so_5::send is used for signal sending:

so_5::send< my_signal >( mbox );

Usually it is necessary to send messages to the agent's direct mbox. So instead of writing:

so_5::send< msg >( agent.so_direct_mbox(), ... );

it is possible to use so_5::send_to_agent function:

so_5::send_to_agent< msg >( agent, ... );

There are so_5::send_delayed functions for sending delayed messages/signals:

// Sending delayed message.
so_5::send_delayed< my_message >( mbox, pause, some_args );
 
// Sending delayed signal.
so_5::send_delayed< my_signal >( mbox, pause );

There are so_5::send_delayed_to_agent functions for sending delayed messages/signals to an agent's direct mbox:

so_5::send_delayed_to_agent< my_message >( agent, pause, some_args );
so_5::send_delayed_to_agent< my_signal >( agent, pause );

There also are so_5::send_periodic functions for sending periodic messages/signals:

// Sending periodic message.
so_5::send_periodic< my_message >( mbox, pause, period, some_args );
 
// Sending periodic signal.
so_5::send_delayed< my_signal >( mbox, pause, period );

There are so_5::send_periodic_to_agent functions for sending periodic messages/signals to an agent's direct mbox:

so_5::send_periodic_to_agent< my_message >( agent, pause, period, some_args );
so_5::send_periodic_to_agent< my_signal >( agent, pause, period );