limitations of spanned text formatting

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 With markdown, unsupported syntax could still be written with an outdated client and it would still work.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.