Create common class for tags

[GoogleCodeExporter]

There are several different tag structures, like Exif, IPTC and Photoshop
in JPEG and TIFF files. But each of them finally boils down to a number, a
position in the file, and a length. Currently, each different metadat type
class implements this on it's own, but there should be a common class to
handle these tags.

Original issue reported on code.google.com by p.edel...@gmail.com on 15 Mar 2007 at 8:06

[GoogleCodeExporter]

This class can also be used for handling larger data structures, like JPEG 
segments.

Original comment by p.edel...@gmail.com on 15 Mar 2007 at 5:08

[GoogleCodeExporter]

The class should also offer the facilities to manually set data and bytewise 
reading.

Original comment by p.edel...@gmail.com on 15 Mar 2007 at 7:17

[GoogleCodeExporter]

This is now done in the class Tag of file tag. It supports both data on disk 
and in
memory, and provides methods to:
- set data
- get data
- get length of data
- get offset of the data in the file
- read part of the data or the entire block

It functions as the base class for
- JPEG Segments
- Photoshop data
- IFD tags

Original comment by p.edel...@gmail.com on 16 Mar 2007 at 10:15

• Changed state: Fixed

[GoogleCodeExporter]

To avoid confusion, this class has been renamed do DataBlock in the file 
datablock.py
It also better covers its function.

Original comment by p.edel...@gmail.com on 18 Mar 2007 at 8:59