define convention for expressing Matroska fragments in readable text

[dericed]

For instance to explain the examples in here https://github.com/Matroska-Org/matroska-specification/blob/3e689519b9a84e508d98b1dcbd97d17744e144a3/chapters.md#example-1--basic-chaptering. This issue supersedes this discussion.

[robUx4]

That seems to be more related to expressing EBML "fragments" in readable text. Once we have that Matroska can use it. It may refine how to define certain Binary data like the Block and BlockSimple.

[robUx4]

IMO this should be in a separate document. There can be many formats to describe a binary format in text (json, xml, yaml, etc). That should influence (or block) how the binary format is defined.