Add delete command.
Fix setup.py and minor errors.

Fix entry_points in setup.py and change 'import engine' to
'import refile.engine'. Also change 'rename' to 'delete' in setup_delete.
Change SEARCH to PATTERN in engine.

Caused `refile print` and `refile delete` to send incorrect arguments to
__init__().
Change subcommand names.

Change them to be more in line with UNIX command line utiliies.
'Fix' problem with program once installed.

Once installed the program did not print a useful error message when called as
`refile` with no args.