Daemon to generating kline data and API to get kline data

1. run `rake daemon:k:start` to generat k data in background
2. k-line data is stored in redis' list named `#{market}-k#{period}`
3. visit `/api/v2/k?market=btccny&limit=10&period=30&timestamp=1403236860` to get k-line data


cc @janx 
Redis should be configed with `ENV['REDIS_HOST']` or a new env var, otherwise the code won't work on production servers, where redis is located on a different server.

Check https://github.com/peatio/peatio/blob/master/config/environments/production.rb#L56