General improvements

[leandromoreira]

Shorten the key_prefix

Let's say we want to count 200K users or tokens, it implies the double of the counters (past and current minute) multiply that by 18 (key_prefix length), maybe we can use something like nrm.

• (4e5 * 18)/1024^2 6MB vs 1MB (4e5 * 3)/1024^2

Uncouple ngx from measure function

It can be useful outside of nginx, we can change the function signature to also receive the current_time in seconds.

Generate docs

http://stevedonovan.github.io/ldoc/

[leandromoreira]

Improvement 2 is not possible due ngx.null and redis-resty openresty/lua-resty-redis#65