Add Adobe Photoshop (PSD) file format

[davidhicks]

Official specification of the Adobe Photoshop (.psd) file format: https://www.adobe.com/devnet-apps/photoshop/fileformatashtml/

Work in progress branch for implementing a Kaitai Struct format specification for .psd: https://github.com/davidhicks/kaitai_struct_formats/tree/psd

[davidhicks]

Status update on the draft ksy specification:

• most features of the file format which are officially specified have already been implemented in the draft ksy specification
• one of the fields of the file format pulls in an ICC (version 4 I think) file, and I can't work out how to get https://ide.kaitai.io to find the existing icc_4.ksy file in the official formats repository using the import syntax
• there could be a bug where the draft spec tries to define an infinite recursive data structure related to the descriptor_resource type (commonly used data structure within the Photoshop format)
• I haven't yet seen a need for additional features to be added to Kaitai Struct before this file format specification is completed

[GreyCat]

We had an idea of alternative one-repo-per-file-format development model for bigger, more important formats that require lots of careful planning, testing, storing samples, etc, etc.

Generally, under this model, development of such "big" formats happens in separate repo that gets merged into kaitai_struct_formats periodically.

I guess I shall create a separate issue for disucssion of this approach, and I totally want to invite you to try it with Photoshop file format project. This should aid collaboration on such non-trivial formats immersively.

[GreyCat]

Ok, here we go: kaitai-io/kaitai_struct#165

[GreyCat]

Alternative PSD spec implementation from @ertaquo:

https://gist.github.com/ertaquo/b1d12c37a21268e3d095d39e196f5863

[KOLANICH]

Also https://gist.github.com/vladdancer/832aec8790995a5676dae0839993807a