add `pointOnBoundary` check

[tmpvar]

containsPoint has been fixed to do a proper containment check. Which means, it no longer resolves intersections with the boundary as "inside". Segment2 has the appropriate machinery to do a on line check.

[tmpvar]

Better bet is robust-orientation

[dbtek]

Any update on this?

[tmpvar]

I haven't taken the time to implement it, but it shouldn't be that bad. I was thinking about doing something with http://github.com/mikolalysenko/robust-orientation to provide this functionality.

I'd be open to a pull request if you have time!