Feature Request: Add an option --list-included

[pasman1]

Hi.

I think, that it be useful to add an option to list tasks
from included taskfiles. It will allow to view all available tasks.

For example:

task --list-included='*' - list tasks from current and included taskfiles
task --list-included=':' - list tasks from current taskfile
task --list-included='namespace' - list tasks which begin with 'namespace'

Best regards.