Merge pull request #2 from Zash/master

base: Previous commit popped an item too much.
luaevent.c: Drops global registration of core in favor of reducing global pollution
luaevent.lua: updates version specification to the next release version
event_callback: Fix segmentation fault

If an event is closed and an error occurs in the same callback, it would
cause a segfault due to cb->base being NULL
event_callback: Keep declarations at the top
core: updates to MIT-style license and properly includes in file heading
Merge pull request #3 from Zash/fix-segfault

event_callback: Fix segmentation fault
core: fixes header definition to use luaopen_luaevent_core