get transformation args with underscore

[a-salimkhanov]

Useful when you are proxying requsts from NGINX, like

location ~ "^/image/(?<tr_options>[^/]+)/(?<image>.+)$" {
    proxy_pass http://localhost:8888/?url=http://backend/$image&transformation=$tr_options;
}

So you can have img links like:
http://example.com/image/w_300,h_100/some.png

[coveralls]

Coverage increased (+3.08%) to 98.932% when pulling 250102e on a-salimkhanov:patch-1 into d05d1c0 on agschwender:master.