Changes for version 0.5
- add signal and pid mutators.
- add rstatus/rpid accessors.
- updated libev (lower cost for clock monotonic).
- support event priorities.
- try to find SIG_SIZE on perls that don't have it (Slaven Rezic).
- improved signal handling, fixed child watchers.
- experimentally add kqueue backend, completely untested.
- ported to cygwin and native win32.