First version of Downing-Gallier

seems to do what it should, but definitively needs more testing

Signed-off-by: Daniel Borchmann <daniel.borchmann@mailbox.tu-dresden.de>
Downing-Gallier goes into downing_gallier.clj

and not linclosure.clj

Signed-off-by: Daniel Borchmann <daniel.borchmann@mailbox.tu-dresden.de>