Restore documentation of MySQL event structures

Until 0.10, the change events structure section had detailed info on update and delete events. In the current version (beginning with 1.0), this information is missing.

There still are examples for update and delete events, but all the explanatory parts got dropped, I suppose in the course of the modularization rewrite.

In addition, the version in the source part of example events is hard-coded now: "0.10.0.Beta4". Instead, it should be the AsciiDoc attribute "{debezium-version}" to always reflect the current version.