Great. Would you guys like to leave it open as a community thing, or would you like to put this somewhere and organize tasks as a team?
I think we'll leave it open atm.
If you have wishes of something particular you want to do, just say it an do it.
I don't think a core team is necessary yet, we are so few. Those who ever looked at the source are probably inside the core team

Priority now is probably the collision response, but don't go and do big stuff until I upload what I already have done.
If you absolutely want to, here are the functions you could use:
functions.place_free(x, y, wallmask)
Obvious, checks whether a point is free in the wallmask.
objectCheckCollision(character, wallmask)
Checks whether that object hits the wallmask somewhere.
Actually, I've already improved it a bit compared to what I just posted before, and I'm almost done with getting a git repos ready.
I'll upload everything as soon as I get home.