Make dashback configurable, fix movement bugs, add double jump forward and back.

src/math/segment.rs

@@ -141,6 +141,15 @@ impl FGSegment2d {
             None
         }
     }
+
+    /// Returns a value representing the normalized position along the segment.
+    pub fn project_point_normalized(&self, point: FGVec2) -> FGi32 {
+        let segment_vector = self.point2 - self.point1;
+        let offset = point - self.point1;
+        // The signed projection of `offset` onto `segment_vector`, scaled by the length of the segment.
+        let projection_scaled = segment_vector.dot(offset);
+        FGi32::from_num(FGWide::from_num(projection_scaled) / segment_vector.length_squared())
+    }
 }
 
 #[cfg(test)]