Unarchiver.search method added

It searches for RAR archives in a given directory.
Unrar#extract's unrar command updated

Unrar doesn't overwrite existing files on extraction now. It speeds up
and simplifies execution.
Unarchiver.extract method added
Unarchiver.extract_from_path method added
Rack-test gem added
ExtractJob added

It is Resque job which extracts an archive from
a given path.
POST /extract call added
ExtractJob updated with destination path parameter

App should provide destination path for a job. It
should be stored in config file.
Script for adding an extract job