create non-annotated tags

The release process works as follows:

 1. Create a commit where the the version number (in configure) is
    updated.  This commit should have the commit message

      version <version>

    where <version> is of the form x.y.z with x = major, y = minor, z
    = patch level.

 2. Run configure

      ./configure --disable-meta --disable-compile --with-models-=

 3. Create a non-annotated tag via

      make tag

    A tarball and a correspondin .md5 file will be created.