[ENH] Function for converting PAG to MAG

[aryan26roy]

Closes #85

Changes proposed in this pull request:

• Adds a function for converting PAGs to MAGs.

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[adam2392]

I think you want a function that goes MAG to PAG?

A PAG has many MAGs possibly associated with it.

[aryan26roy]

Ah ok. This for after the MAG has been validated in #73.

[adam2392]

Can you describe the algorithm in the PR description?

[aryan26roy]

@adam2392 moving the discussion to #87