Create automatic cache compile code similar to scssphp's Server

[zimzat]

Currently lessphp leaves it up to the user to check the cache object and file access times to determine if it needs rebuilt. It also leaves it up to the user to serialize and store the cache object.

On the other hand scssphp provides a Server object which handles this internally, leaving the user free to ignore how the cache works. There is an issue open to expose this ability through explicit in/out filenames that I'm looking to implement. https://github.com/leafo/scssphp/issues/215

Would it be feasible to incorporate similar functionality into lessphp so that the two libraries have similar usage signatures? I can make the change and do a pull request for this if so. If so, should the functionality be incorporated directly on the lessc class, or would you recommend putting it somewhere else such as a lessc_server?