Allow custom attributes in .ksy files

[scallacs]

It would be nice to allow custom attributes in the .ksy definition file.

We could prefix these attributes with x- like OpenAPI does.

meta:
  id: my_id
seq:
  - id: myfield
    type: u4
    x-custom: my custom value

This is usefull to easily add extra informations and develop extensions.

Currently IDE throws an error when a non expected attribute is found is .ksy file:

io.kaitai.struct.format.YAMLParseException: /seq/0/x-custom: unknown key found, expected: consume, doc, doc-ref, eos-error, id, if, include, repeat,

[KOLANICH]

Custom attrs are prefixed with -.

-custom: my custom value

and the bug tracker about the language itself is kaitai-io/kaitai_struct , this one is webide-related.

[scallacs]

Oups a did not search enough! Thanks!