Access module using HMAC

Hi!

This is not really an issue but I wanted to let you know that I've reused and adapted your module to turn it into an access module to authorize/deny some locations based on a HMAC. I'm not sure how I'm supposed to submit a new Nginx module but I thought you might be interested so here it is: https://github.com/Meteo-Concept/ngx_http_hmac_access_module :-)

