Commands like show and complete should allow a filter argument

[mehmetseckin]

This will enable non-interactive use, e.g.

todo show refactor would show everything with refactor in it.

todo complete registration will complete everything with registration in it.

[Regenhardt]

For show/list, this can usually be achieved already by piping the output into grep (or the powershell equivalent) like todo list --all | grep refactor. I did however add a --list filter in #23 to the list and complete commands to only list or complete tasks from a specific list.