Remove outdated examples.
Refer to fields by name rather than position in a record header.

When describing a record header, refer to null, variable-length or
extern fields by name.
Refactor index record format description to describe each and every field in the index.

Build record format descriptions based on the record type (node or
conventional) and add system fields where appropriate. This fixes
an issue where the header of node records of a clustered index would
be improperly read due to row fields being included in the record
format description.