Auto-fallback to list options if argument not provided

[DarthBenro008]

Right now you need to provide an positional argument to rchore tasks done <pos> or rchore tasks delete <pos>. It would be really nice if you could fall back to a list option presented to the user when the position is not passed, something like what already rchore task-list update or rchore task-list delete does.

Sample:

Relevant Codebase: https://github.com/DarthBenro008/rchore/blob/2561389ceed92cfbddc727eadf04586c3d62e87d/src/handlers/task_handler.rs#L109-L127

https://github.com/DarthBenro008/rchore/blob/2561389ceed92cfbddc727eadf04586c3d62e87d/src/handlers/task_handler.rs#L74-L95