Changes in version 0.28:

Support for PNG images has been implemented using libpng.

The variables AR and ARFLAGS can now be set from configure. (Before you
needed to run 'make AR=<ar_command>'.

The version test macro OCRAD_API_VERSION and the function OCRAD_api_version
are now declared in the header file ocradlib.h. They tell to the application
the version of the library.

Many minor fixes and improvements have been made.
