adds rm functionality

Addresses #3 

rm: Remove a file or directory at the given Google Drive path.
Arguments: [-r, -s] <drive path>,
where files and directories are recursively removed if -r is specified
and the google drive trash is skipped if -s is specified. The default 
behavior is to file if the drive path specified is a directory and -r is 
not specified, and to send files to the trash instead of permanently
deleting them.