[WIP] Introducing PCS codebase as a separate module

[storojs72]

Partially fixes #304.

Reorganises PCS codebase into a separate module.

Moves vanilla KZG10 utilities from ZM.

Still work in progress

[huitseeker]

I think the commitment-related¹ parts of :

• kzg_commitment.rs
• pedersen.rs
  should stay out of the PCS module, because the traits they are dedicated to implementing are unrelated to the EvaluationEngine. They could be in their own commitment module if you like.

Footnotes

1. I do not consider the implementation of CommitmentKeyExtTrait for the pedersen commitment to be commitment-related, and in fact it's only used by the IPA. So that trait implementation could move to the PCS module. ↩