Create a unified ownership trie.

[NathanFrench]

There is no real regulation other than take_ownership that allows for a user to specify who owns what (e.g., who opens and closes a file descriptor).

See initial discussion: #6

Cascading the structures and adding a flag would be optimal:

struct socket {
   int flags; (EVHTP_SOCK_OWNER)
   int sock;
};

struct evhtp {
    int flags; (EVHTP_FLAG_OWNER)
    struct socket socket;
     ...
};

struct connection {
   int flags; (EVHTP_CONN_FLAG_OWNER)
   ...
};

struct request {
   int flags; (EVHTP_REQ_FLAG_OWNER)
   ...
};

[NathanFrench]

Added https://github.com/criticalstack/libevhtp/compare/merge-flags branch to track this.

[NathanFrench]

#12 addresses half of the fun - going to merge this part if nobody has a problem.