add resty.uuid wrapper

[smallfish]

Example:

local resty_uuid = require "resty.uuid"
local uuid = resty_uuid:generate()
ngx.say("uuid: ", uuid)

Require:

libuuid

[subnetmarco]

+1

[agentzh]

Because lua-resty-string is already a mess. This better to be in a separate library like lua-resty-uuid. Thoughts?

[subnetmarco]

Having it in a separate library sounds good to me

[smallfish]

@thefosk try https://github.com/bungle/lua-resty-uuid ?