rules/equalityᵒ: Implement even? and odd? transformation rules

This addresses a part of #4.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
rules/equalityᵒ: Implement none? => nil? rule

This addresses another part of #4.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
rules/equalityᵒ: Fix the nil? rule

It was lacking some unquotation.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
rules/syntaxᵒ: Add an isinstance => instance? rule

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
rules/syntaxᵒ: Add a few (instance? type x) => (type? x) rules

This addresses a few points of #4.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
rules/syntaxᵒ: Add a yield-form rule

The previous changes and this together fix #4.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>