Give access to SWC comments

[mgeplf]

Both SWC+ and @Helveg use the header of an SWC file to store metadata. To simplify their use case, perhaps we should give access to comments via annotations for SWC files.

[Helveg]

Any progress here? Since the new parser came through I think this is the last blocking issue for the BSB (https://bsb.readthedocs.io/en/latest/) to deprecate its own parser and use MorphIO as its default parser

[mgeplf]

Unfortunately, I haven't added that feature yet. With the new parser, it should be easier, but I need to find the time.