tests: More Reasoned Schemer tests

This adds a few more tests, and turns unbound into a function.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Fix (fresh)

Calling (fresh [x]) twice should produce two distinct fresh LVars, so
use a bit of gensym magic to make it so.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
tests: Chapter 1 of The Reasoned Schemer covered

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>