review the stdout/err messages

[Raffaello]

• The library should not write on stdout/err but should be the app/program.

• the library should only produces logs and call the message callback that must be set up by the program otherwise no writing.. ?

• at the moment it is challenging to just add the compression ratio while encoding within the [ OK ] message for e.g. as that information at that point is not available anymore in the library. (besides the library shouldn't write on stdout)

• also if the library should be used with a GUI it would be fairly complex to update GUI component in that way.