Python-exiv2

1/ Add Exiv2::PreviewManager to Python interface.

1/ Binary wheels use libexiv2 version 0.27.5.

1/ Fix several memory leaks.
2/ Create binary wheels for MacOS (as well as Linux and Windows).
3/ Fix problems installing on MSYS2 / MinGW.

1/ Fix undefined symbol problem with Linux binary wheels.
2/ XmpProperties.registeredNamespaces() returns a Python dict.

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* Exiv2 utility

* Added -pI print mode to print Iptc data.

* Bugfix: Use timegm() and gmtime() instead of mktime() and
localtime() to avoid problems when adjusting timestamps.
Thanks to Samir Rostum for pointing out this bug.

* Added timegm() from the tz distribution for platforms which
do not have this function.

* Exiv2 library

* Added full Iptc read and write support. Thanks to Brad Schick for
this and a lot more contributions to this release.

* Converted Metadatum to an abstract base class, added Exifdatum
and Iptcdatum classes. Migration of existing programs: Use class
Exifdatum instead of Metadatum. (Brad Schick)

* Added Key, ExifKey and IptcKey class hierarchy. Requires changes
to existing pograms: Use class ExifKey where plain std::string
keys were used before (e.g., ExifData::findKey()).

* Changed Exif keys to 'Exif.ifdItem.tagName' to be consistent
with the new Iptc keys. All keys of existing programs need to be
updated. See the web pages or documentation for the new keys.

* Revamped class Image and introduced byte* interface. (Brad Schick)

* Added autoconf configure script.

* Added MSVC project files. (Brad Schick)

* Appended 'Id' to Ifd ids to work around a g++-3.4 problem.

* Updated documentation.

1/ API change: data iterators no longer have a "curr" method, as all the
methods of the datum it returned are directly accessible.
2/ The BasicIo class and its subclasses are no longer available from Python.