MIF Filter: extract cross-references as codes

[Denis Konovalyenko]

It has been revealed that:

1. All cross-references (XRef) are based on one or another format (XRefFormats)
2. All cross-references are rendered in precise accordance with predefined formats and updated automatically if a related format has been changed. It is not allowed to change cross reference presentations other than by editing their formats.

Consider a revert of issue #991 followed by a code extraction implementation of XRef - XRefEnd tags. For more details please refer to the attached sample document:

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[Denis Konovalyenko]

A related pull request #560 was opened.