Changes 0.23:
* Exiv2 utility
  - Allow to add/set tags without a value with the command line tool.

* Exiv2 library
  - 0000819: Recognize Pentax MakerNote in DNGPrivateData (Jonathan Kollasch)
  - 0000815: Patch for Tokina 11-16mm f/2.8 on Canon (Chris Chiappa)
  - 0000812: Exiv2 destroys hard links (Reported by Anders Kamf)
  - 0000811: Typo in de.po (Thomas Beutlich)
  - 0000810: assert(tiffType() == ttUndefined) error in tiffcomposite.cpp
            (Reported by Auke Nauta)
  - 0000809: abs ambiguity in nikonmn.cpp (Pavel Heimlich)
  - 0000808: build failure in jpgimage.cpp - namespace (Pavel Heimlich)
  - 0000807: spelling-error-in-binary usr/lib/libexiv2.so.9.0.0
            Continous Continuous (Mark Purcell)
  - 0000806: spelling-error-in-manpage src/exiv2.1 explicitely explicitly
            (Mark Purcell)
  - 0000803: Rational/URational issue in convert.cpp (Pavel Heimlich)
  - 0000800: Missing Photoshop IRB types (8BIM, PHUT, DCSR, AgHg)
            (Michael Ulbrich, Volker Grabsch)
  - 0000799: Exiv2 returns wrong XMP type for nested XMP keys
  - 0000798: Add MS Photo RegionInfo and MetaWorkingGroup Regions schemas
            (Benjamin H.)
  - 0000797: A crash can occur with certain JPEGs. (Clint Rogers)
  - 0000795: Set/Get of PNG comment (Reported by Thomas Beutlich)
  - 0000794: Typo in exifFlash description (Thomas Beutlich)
  - 0000793: PNG comment is not set (Thomas Beutlich)
  - 0000792: New Canon Lens EF-S 18-55mm f/3.5-5.6 IS II (Andreas Ferber)
  - 0000791: Tamron SP AF 17-50mm F/2,8 XR Di II LD Aspherical [IF] Nikon lens
            (Philip Johnsson)
  - 0000790: XMP embedding corrupts CorelDRAW EPS files
  - 0000778: Add support for Windows Live Photo Gallery face tags (Leif Huhn)
  - 0000635: [Wish] Write support for Canon RAW CR2 files
          - Updated Nikon Lens lookup table to v4.3.428.01 of
            Robert Rottmerhusen's fmountlens list.
          - Added support for Nikon3 AF Fine Tune array. (Frans van den Bergh)
          - Added Canon EF-S 18-55mm f/3.5-5.6 III lens. (Jon Charnas)
          - Fixes to buildForMac to work with 0.22 on Leopard and Lion
            (Robin Mills)
          - Added several KIPI XMP properties (Gilles Caulier)
          - Added cmake patch to fix compilation on MSVC with KDE Windows
            (Ananta Palani)
          - Fixed the supported metadata declared by the Image for several
            image formats (mostly XMP was missing).
          - Added support for CR2 IFD2 image preview. (An uncompressed TIFF
            image without white-balance correction.)

(adam)