Unifiy callout, heartbeat and various funciton as an tick_event loop.
Migrate more internal stuff into options_internal.h
Make comment for APPLY_CACHE_BITS more obvious
Improve hash function for apply cache.

This seems to reduce collisions and should provide better
performance.
Added a TODO to handle LPC runtime error more elegantly.
Remove duplicated sig_hup handler.
Clear tick_events queue on exit.
Register auto reclaim_objects() call.
Update travis config.