fs_c.lua: fs.delete => fs.rm, do more check for fs.mkdir
util_c.lua: add util.strlen
event.lua: event:destroy() for non-io event
fs.lua: add fs.abspath
generics.lua: unify code format for remove 1 element from array
shmem.lua, thread.lua: implement thread.lock_shared_memory and remove element by specifying nil to second argument of thread.shared_memory