core: Use a shorter param for simplify-expression

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
core: Rename simplify-expression to simplify-step

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
core: Prune unused imports

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
core: Split out some functions into hydiomatic.utils

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
core: Optionally allow specifying rules for simplify-step and simplify

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