limitations of spanned text formatting

[bluskript]

The formatting system we have now currently has clients provide text ranges to format in specific ways. This has a few flaws compared to markdown which should be addressed:

1. Harder to upgrade. Clients will need to update their text inputs to make it possible to use new formatting capabilities. Increases maintainer workload. With markdown, unsupported syntax could still be written with an outdated client and it would still work.

2. Impossible / Inconsistent on some platforms. Bridges from other services will face issues with formatting, because of how on most of them the formatting is fundamentally text-based.

[sowelipililimute]

1. clients can just display a format for unsupported formats no problem, which will have the same amount of meaning as unknown symbols to a user.
2. this is actually the easiest format for bridging: all the data is already in a convenient format, ready to be made into whatever format the service can work with, which isn't necessarily markdown. incompatible formats can be discarded or converted into other formats via simple manipulation of span objects instead of trying to manipulate a CST for markdown, or unparsed markdown.