Removal function of unnecessary vertices

1. Reduce unnecessary vertices near T-junctions and crossroads, so that most intersections meet at a single point.
   
   ↓After post-processing
   
   
2. By corner sharpening, the vertex of corners becomes a single point regardless of acute or obtuse angles.
   
   
3. Removal function of unnecessary vertices on straight lines which eliminates almost all unnecessary vertices on straight lines.
   
   
4. Removal function of whiskers that occur at the tip of acute angles.
   
   ↓After post-processing