More file renames to improve code navigability.

[m-renaud]

Description of change

File renames only.

• identity-iota/src/chain/document.rs -> identity-iota/src/chain/document_chain.rs
  • DocumentChain (no change)
• identity-iota/src/chain/diff.rs -> identity-iota/src/chain/diff_chain.rs
  • DiffChain (no change)
• identity-iota/src/chain/integration.rs -> identity-iota/src/chain/integration_chain.rs
  • IntegrationChain (no change)
• identity-iota/src/did/doc/diff.rs -> identity-iota/src/did/doc/document_diff.rs
  • DocumentDiff (no change)
• identity-did/src/diff/document.rs -> identity-did/src/diff/diff_document.rs
  • DiffDocument (no change)
• identity-did/src/diff/method.rs -> identity-did/src/diff/diff_method.rs
  • DiffMethod (no change)
• identity-did/src/diff/service.rs -> identity-did/src/diff/diff_service.rs
  • DiffService (no change)
• identity-did/src/diff/did_key.rs -> identity-did/src/diff/did_key_diff.rs
  • Contains Diff impl for DIDKey (no change)

Links to any relevant issues

#218

Type of change

• Enhancement (a non-breaking change which adds functionality)

How the change has been tested

cargo test

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• New and existing unit tests pass locally with my changes