Add support for cbr format

[zackad]

Possibly using this library https://github.com/selective-php/rar

edit: Unfortunately that library only for listing rar archive entry. Not able to retrive the content either as resource or load directly into memory. We still need PECL rar extension that might not be trivial to install in some environment.

[zackad]

Honestly I don't want to implement this. I don't want to encourage/facilitate poeple to use non-open/standard format.