util.signal: Add support for signalfd(2) on Linux signalfd allows handling signal events using the same method as sockets, via file descriptors. Thus all signal dispatch can go through the same main event loop as everything else, removing need for thread-scary signal handling where execution would just jump to the signal handler regardless of the state of Lua, and needing to keep track of Lua states/threads.

== 1.0 ==
- Roster providers
- Clustering
- World domination