ENH: Add three new workbench command interfaces

[a3sha2]

I added the following interfaces for workbench

• [x] wb_command -cifti-correlation
• [x] wb_command -cifti-parcellate
• [x] wb_command -cifti-separate

[effigies]

@a3sha2 I'm going to try to make a release in the next couple days. If you want to try to finish this off, I'd love to include it!

[a3sha2]

sorry for delay @effigies, I will fix it this week

[a3sha2]

@effigies I added test data

[a3sha2]

I will work more on test dataset