custom max age by url

Add a way to make possible configure a max age value to be used on result image that override the server default configuration.

The value must be set as a common operation.
For instance, /unsafe/40:30/age:60/image.jpg will produce an image of 40x30 pixels with 60 seconds of max age.

This option gives flexibility to the user set different max age values without lose the security, since the new option will be encrypted during the signing process also.