Make coro::net::ssl_context a shared_ptr when used with schedulers and clients

[jbaldwin]

Right now in the example test_tcp_server.cpp:85 it passes the ssl contexts into the schedulers and clients by reference, this should ideally be by shared_ptr copy since the lifetimes are now bound.

[jbaldwin]

I'm not sure this is the right thing to do now, perhaps each client or server should make their own context and just own it? I think my original idea was to allow the user to pass it between clients or servers to re-use them, but I think this makes the lifetimes ambiguous.

[niansa]

I agree. But at the very least it should accept a reference instead of a pointer - using raw pointers in C++ is known as bad practice.

[jbaldwin]

I'm planning on dropping ssl support since it doesn't really seem necessary, and I don't have the time to support it, so going to close this one out.