rules/equalityᵒ: Add an (if-not (is ...)) => (if (is-not ...)) rule

This rule turns (if-not (is ...) ...) into (if (is-not ...) ...), which
is more efficient. This addresses the second half of #9.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
hydiomatic/rules: Change the order of equalityᵒ and control-structᵒ

In order to pick up the new (if-not (is ...)) => (if (is-not ...)) rule
during a full simplify, pull rules/equalityᵒ up above
rules/control-structᵒ.

Together with previous changes, this fixes #9 completely.

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