This changes the licence of Loko Scheme to EUPL-1.2-or-later: the
European Union Public Licence version 1.2, or later.

The EUPL 1.2 has several benefits over AGPL-3.0-or-later, which was
the previous licence. The EUPL follows a different legal tradition
with regard to linking. This tradition is one which is much more
suitable for a compiler that embeds its runtime in its output, like
Loko Scheme does. Please read the EUPL for more details. There is also
some guidance in the manual.

The source code should now also be compliant with the REUSE
specification. A very recent version of the reuse tool is needed to
support the SPDX license identifier "EUPL-1.2+".

Signed-off-by: Göran Weinholt <goran@weinholt.se>