[Feature]: Add a new module vfox.cache to allow plugins to cache something.

[aooohan]

2. What is your expected outcome?

Something like below:

local c = require('vfox.cache')


local cache = c.new('path')

--- -1 : never expired
cache.set(key, value, expire_time)

local value = cache.get(key)

local success = cache.remove(key)