Implement a list method

[arolett2]

This change implements a barebones list method to let users see what files exist on their drive (a nice complement to the pull function).

Right now it just dumps a list of files and directories: If the path is a file then it is listed. If the path is a directory then the direct children are listed.

Note this partially address issue #9.

Future work. Add options to list details about files in the cloud. Make it so users can tell files and directories apart.