Adding a Scheme script to extract the required information from the xcf files in order to replace xcfinfo.
Adding the license header in info.scm.
Moves the calls to the GIMP in an independant class.
image_generator uses the gimp_interface class to execute its script.
The xcf informations are extracted using the new gimp_interface. XcfTools is not required anymore.
Updating the man page to remove the --xcfinfo argument.
The extraction of the XCF informations handles the layer groups.
Fix how the GIMP's version is computed.