Provide better support to manipulate meta data (chunks)

[Google Code Exporter]

Some more high level methods are needed (and examples/tests) to edit meta data, 
in chunks:

 setDPI()
 addTextComment(keyword,content)

Palette creation. 

Also, a more flexible mechanism is needed for the programmer to specify some 
strategy for copyin chunks from the reader to the writer. 
PngWriter.copyChunks() is a first step

Original issue reported on code.google.com by [e-mail] on 29 May 2011 at 9:03

[Google Code Exporter]

setDPI / getDPI done

Original comment by [e-mail] on 15 Jun 2011 at 2:16

• Changed state: Started

[Google Code Exporter]

PngMetadata added. This includes now high-level management for PHYS (DPI),Text 
annotations (TEXT ZTXT ITXT), and TIME

Original comment by [e-mail] on 3 Apr 2012 at 3:15

[Google Code Exporter]

done in version 0.9

Original comment by [e-mail] on 14 Apr 2012 at 1:21

• Changed state: Fixed