Rules: no such thing as "do" and built-in-functions

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Rules: no such thing as user-defined functions.

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Rules: remove redundant comment-cruft

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Rules: various boilerplate-ish stuff

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Rules: implement reserved words boilerplate

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Rules: add comment explaining absence of portage_slot function

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Rules: easy lexing parts

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>