Adding nginx build script

Fixes #63.

Run "bundle install", then ./build/nginx.sh. New nginx package will be in the tmp subdirectory. 

It has no dependencies or config files flagged. You most likely need to have at least:

* libgeoip1
* geoip-database
* libpcre3

It installs into /opt/nginx. Most likely you'll want to start it with a specific configuration file/directory, which points to your actual config file location.