Merge branch 'doc_dal' into 'dev'

blockchain/apply_valid_block.rs

blockchain/revert_block.rs

dal/balance.rs

dal/block.rs

dal/constants.rs

dal/currency_params.rs

dal/dal_event.rs

dal/dal_requests.rs

dal/identity.rs

dal/lib.rs

dal/parsers/certifications.rs

dal/parsers/mod.rs

dal/parsers/revoked.rs

dal/sources.rs

dal/tools.rs

dal/writers/block.rs

dal/writers/certification.rs

dal/writers/dividend.rs

dal/writers/identity.rs

dal/writers/mod.rs