Remove underscore versions of all parameters

[tsalo]

Closes none. This is a breaking change because parameter names have effectively been changed.

Changes proposed in this pull request

• Remove underscore versions of all parameters (e.g., --anat_only instead of --anat-only).
• Add dash versions where they were missing.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 28.57%. Comparing base (0e21c37) to head (6ab3975).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #861 +/- ## ======================================= Coverage 28.57% 28.57% ======================================= Files 68 68 Lines 10126 10126 Branches 1135 1135 ======================================= Hits 2893 2893 Misses 7134 7134 Partials 99 99 ```

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[tsalo]

Oh you're right! I might have corrected in the wrong direction. Do you have any issue with me reversing this and dropping the underscore versions?

[mattcieslak]

I trust the fmriprep folks on this decision

[tsalo]

Okay cool, I'll reverse my changes.