Version 21 of this C API has changed from version 20 as follows:
L_OcrPageSortedZonesIndexMapOptions
L_OcrEngine_GetRuntimeFileCallback
L_OcrEngine_SetRuntimeFileCallback
L_OcrPage_GetSortedZonesIndexMap
L_OcrCharacter - Takes 5 new members.
L_OcrDocumentFontType - Takes 8 new enumerations.
L_OcrWord - Takes 2 new members.
L_OcrZoneType - Takes one new enumeration.