Creates lua user data cache_ud.

Golang

	state := lua.NewState()
	cache.Preload(state)
	// register user data "cache"
	cache.NewSqlite(state, "cache", "/tmp/db.sqlite")

Lua

cache:set(string, number)

Set number to cache by key string, raise error.

cache:get(string)

Get number (value) and number (time updated_at) from cache by key string. Return two number or two nil, raise error.

cache:diff_and_set(string, value)

Get number, diff from previous value. Return number or nil, raise error.

cache:speed_and_set(string, value)

Get number, speed based on previous value. Return number or nil, raise error.