High level interface with (custom) futures

[daniele77]

I'd like to write a sequence of aricpp operation in this way:

ch1->Hangup()
.Then([=](){ return bridge->Destroy(); })
.Then([=](){ return ch2->Hold(); })
.Then([=](){ cout << "ch2 in hold\n"; })
.OnError([](exception const& e) {cerr << e.what() << endl; });