build: Generate ChangeLog in 'make dist', ZIP automatically

Change 'make dist' to generate the Git ChangeLog file, that way it doesn't
have to be manually updated nor kept in Git which causes unnecessary work.

Also change 'make dist' to invoke 'dist-zip' automatically to generate a
ZIP as well as a .tar.gz.

Thanks to http://live.gnome.org/Git/ChangeLog for the inspiration to
automatically generate ChangeLog.