MARC relator Inker Penciller Letterer, parser uses non-standard codes

[danielweck]

See description of the problem here:
readium/webpub-manifest#26 (comment)

[danielweck]

Letterer:
https://github.com/readium/r2-shared-js/blob/096a56aa96a030e4f11a4809d9577ab06cfd19ce/src/parser/epub.ts#L1047-L1053

[danielweck]

Penciller:
https://github.com/readium/r2-shared-js/blob/096a56aa96a030e4f11a4809d9577ab06cfd19ce/src/parser/epub.ts#L1054-L1060

[danielweck]

Inker:
https://github.com/readium/r2-shared-js/blob/096a56aa96a030e4f11a4809d9577ab06cfd19ce/src/parser/epub.ts#L1068-L1074

[danielweck]

Commenting the above 3 code blocks will result in defaulting to a generic Contributor + Role (for example if the WebPub code letterer is used in the source publication):
https://github.com/readium/r2-shared-js/blob/096a56aa96a030e4f11a4809d9577ab06cfd19ce/src/parser/epub.ts#L1089-L1096

...However this also means that Metadata.Inker|Penciler|Letterer will never be populated.