Unfortunately the tutorials are all AS1; we never ported that code because we ended up finding a better, simpler approach (and also, the AS1 code is optimized in ways that are useless now).
The ideas in the tutorial still work, there are just better/easier ways to approach it rather than having each tile be a convex shape.
For N v2.0, what we do is generate the line- and circle-segments that are on the surface of the world, then we add that geometry to a grid and use distance-to and ray-intersect queries to collide against it.
We haven't released the source yet, although we gave it to someone for haxeflixel so it should be on a github somewhere (sorry, I can't find the link!). It's pretty straightforward except for generating the geometry on the surface of the tiles, that's a bit tricky... and I suspect there are easier ways to do it than our approach.
Can I just fanboy a little bit and say N was pretty much the reason I almost had to repeat 11th grade, and the Metanet tutorials on collision detection played a huge part in my development as a programmer.