Do not omit from medial axis touching bisectors for narrow angles

With this change, "tails" of narrow polygons defined with just 3 points (rather than a smooth curve) would be retained in output. The condition is that the angle between edges have to be <= 45 degrees for non-inner (touching) bisectors to be retained. The value is currently hard-coded.

I'll add examples to show why this is useful, possibly turned into testcases.