Library Features:
+ Thumbnail support: set (re-calculate)
+ operator>> for Value, since we already have read()?
+ Use auto_ptr where applicable
+ Support TIFF type ids
+ Support for broken IFD makernotes (which have corrupted IFD offsets)
+ Support TIFF images (TiffImage)
+ Support non-intrusive deletion of entries from an IFD.
+ Extended JPEG support (comments, actual resolution of the image)
+ Write an example using low level IFD classes to print summary Exif info

Exiv2 functionality
+ Add offset to value for hexdump (requires metadata to have an offset)

Bugs:
+ Robustness: Ifd::read needs a len argument and before accessing the buffer 
  there should be a boundary check. Similarly in other functions that access
  a data buffer. This should result in a more robust handling of corrupted Exif
  data better (e.g., files with IFD1 but w/o thumbnail, as produced by jhead 
  etc, etc)
+ Handle all Todo's
+ Cleanup and fix implementation of JpegImage (must be able to read any APP0/1),
  should be able to insert exv into extracted thumbs (usually w/o APP0/1)
+ Review Image interface. Is it really necessary to have so many functions there?
+ Review the handling of type ids? What if we encounter type 27 in an IFD?
+ Rational and other output operators (see Josuttis, p653)
+ Through ExifData::iterator and Metadatum::operator= it is possible to have 
  multiple copies of one metadatum in the metadata container
+ Makernote assignment operators
+ Checks and non-intrusive updates must be atomic, i.e., not change anything
  if the metadata is not compatible
+ Review: Exception safety
+ Review: Ifd1 only at Thumbnail, do we really need Thumbnail::update() ?
+ Is the hexdump output of exiv2 byte-swapped??
+ Writing an empty Exif data section should have the same effect as deleting it