Make it build with znc 0.206

Fixes #76.

I'm not proud of the IRCNetwork.h autodetection in the Makefile.  It probably requires GNU Make and GCC and Linux (for /dev/stdin).

It builds and loads (but only if I omit 'curl=yes' when I run make -- looks like a different bug). I can interact with it over IRC, but push notifications to PushBullet fail to work (probably also unrelated to ZNC version).