XMP support
===========
Todo: XMP support is controlled with the ENABLE_XMP directive 
in config/config.mk.in. This will be a configure option
eventually. To build Exiv2 without XMP support, comment the
line "ENABLE_XMP = 1" either in config.mk.in before running
./configure or in config.mk for now.

Top-level Exiv2 classes to access XMP metadata are XmpData,
Xmpdatum and XmpKey. They work similar to the corresponding 
Exif and IPTC classes. The property-repository is XmpProperties.
In addition to the expected new members, class Image also
has a new interface to access the raw XMP packet.

All XMP value types are supported: Simple types, structures,
arrays, property qualifiers and language alternatives.

XMP properties are accessed through keys of the form
"Xmp.<Prefix>.<PropertyPath>", where <Prefix> is the preferred 
(or rather, registered) prefix for a schema namespace and 
<PropertyPath> is the path of the XMP node. In its most basic
form, to address simple properties, <PropertyPath> is the name
of the property. In general, <PropertyPath> can be used to 
address any XMP node, including array items, structure fields
qualifiers and deeply nested properties.

Any properties in known namespaces are supported and additional
namespaces can be registered.

The specialized Exiv2 values XmpArrayValue and LangAltValue are
provided to simplify the use of XMP properties.

See xmpsample.cpp for examples of how to set various types of
XMP properties.

Note: Unlike Exif and IPTC tags, XMP properties do not have
a tag number.

Todo: Conversion between XMP and Exif/IPTC metadata.

XMP Toolkit installation
========================
Exiv2 uses the Adobe XMP Toolkit (XMP SDK) to parse
and serialize XMP packets (only the XMPCore component).

Todo: Integrate the XMPCore component of the XMP Toolkit with
Exiv2 and make the build process transparent for users. The
final solution will be to use an external XMP Toolkit eventually,
once it is available as a standalone package from Linux distros.

Below are the installation steps that worked for me on a
Debian GNU/Linux (testing) system. Your mileage may vary.
Please check with Adobe if you encounter problems with the
XMP Toolkit installation.

Installation directory
----------------------
The top-level exiv2 directory ($HOME/src/exiv2/ on my system).

If you install XMP elsewhere, or use different OS or STAGE
options to the make command below, you will need to manually
modify the exiv2/config/config.mk.in (before running the 
configure script). There is no autoconf-magic yet to set 
this via configure options.

External packages (non-Debian)
-----------------
xmp_v411_sdk.zip    - http://www.adobe.com/devnet/xmp/sdk/eula.html
expat-2.0.1.tar.gz  - http://sourceforge.net/project/showfiles.php?group_id=10127
exiv2               - from SVN

Installation steps
------------------
cd $HOME/src/exiv2/
cp /path/to/xmp_v411_sdk.zip ./
unzip xmp_v411_sdk.zip

cp /path/to/expat-2.0.1.tar.gz XMP-SDK/third-party/
cd XMP-SDK/third-party/
tar zxvf expat-2.0.1.tar.gz
mv expat expat-orig
mv expat-2.0.1 expat

cd ../build/gcc
make -f XMPCore.mak OS=i80386linux STAGE=debug

Expected result
---------------
Now there should be a library
../../public/libraries/i80386linux/debug/libXMPCoreStaticDebug.a
