List only project tasks instead of whole tasks and help message

**Is your feature request related to a problem? Please describe.**

I was using boot for 1st time, and I was searching a command line way for list **only** custom tasks of a project.
After some discussion in slack, people suggested me that `boot -h` do the job.

As user, I didn't saw the project specific tasks because there were to much info which I ignored, when doing `boot -h`

At first glance to me `boot -h` has looked as only an helper command for the CLI itself.

I think the main problem is that `boot -h` is printing to much informations.

**Describe alternatives you've considered**

Maybe a new `-t` for only showing the tasks custom could help.

So the `boot -h` should only show the help of the CLI and `boot -t` should show only custom tasks

Thx for the project!