lib: fix `Sequence::first_index_of`

Signed-off-by: Jean Privat <jean@pryen.org>
nitlight: parse options before initialising modelbuilder

Signed-off-by: Jean Privat <jean@pryen.org>
Merge: fix Nitlight

While messing with #451, I found that nitlight was broken.

These two commit fix it

Pull-Request: #454
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>