adderall.dsl: Implement rememberᵒ

This implements rememberᵒ, and associated tests from The Reasoned
Schemer, chapter 4. Some of the tests are disabled due to bugs and
shortcomings, will revisit those later.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Fix some macro symbol leakage

Fixed (run), (eitherᵍ), and (Zzz) to not leak symbol names through, as
that can corrupt functions run by them.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.lvar: Add a #U reader macro

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Implement appendᵒ

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Implement unwrapᵒ

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
tests: Disable & comment a failing test in the TRS test suite

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
adderall.dsl: Implement flattenᵒ and flattenrevᵒ

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