for libtracker-extract 0.9.21

I. Overview
Core
How to use libtracker-extract — The essentials by example
Data utilities — Functions for coalescing, merging, date handling and normalizing
Common Embedded Support
XMP — Extensible Metadata Platform (XMP)
IPTC — Information Interchange Model (IIM) / International Press Telecommunications Council (IPTC)
Exif — Exchangeable Image File Format (EXIF)
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