Add configuration option for ghost reset distance. Improve documentation.

collisions.cpp

@@ -1,5 +1,6 @@
 #include <glm/glm.hpp>
 
+// Minimal triangle intersection helpers; use local versions to avoid glibc dependencies.
 float abs(float x) {
     if (x < 0) {
         return -x;
@@ -14,6 +15,7 @@ int signbit(float x) {
     return 0;
 }
 
+// Möller–Trumbore style segment-triangle intersection routine.
 int get_intersection(glm::vec3 vec_start, glm::vec3 vec_stop, glm::vec3 P1, glm::vec3 P2, glm::vec3 P3) {
 
     glm::vec3 lba = vec_start - vec_stop;