BOOST and pboted

[polistern]

@majestrate raised very important question about the rationality of using BOOST in the project. The project architecture allows us to replace BOOST with alternatives at this stage.

I prepared small table about used components:

BOOST component	Alternative
program_options	CLI11 (just as example)
filesystem	std::filesystem in C++17 (but then it will be necessary to drop support of old C++ standards)
asio	removed from PacketHandler

Regarding BOOST in parts of libi2pd - these components are not used by the application and have been removed.

I'll post all latest changes soon.

At the moment, I see only one requirement for any BOOST alternatives:
users should not notice any changes and should not be required to make any changes themselves to be compatible with new components.

Decision will be made on the future fate of BOOST in the project after the discussion.

Let me know if anyone has ideas about it.

Thanks