ovl_Obj_Grass_Unit OK and some grass documentation (#1172)

* z_obj_grass_unit OK

* document some grass

* pr suggestions, add grass_unit comment

* pr suggestions

* implement constants

include/z64math.h

@@ -39,6 +39,11 @@ typedef struct {
     /* 0x8 */ s32 z;
 } Vec3i; // size = 0xC
 
+typedef struct {
+    /* 0x0 */ f32 distance;
+    /* 0x4 */ s16 angle;
+} VecPolar; // size = 0x8
+
 typedef struct {
     /* 0x0 */ Vec3s center;
     /* 0x6 */ s16   radius;
@@ -49,8 +54,8 @@ typedef struct {
     /* 0xC */ f32   radius;
 } Spheref; // size = 0x10
 
-/* 
-The plane paramaters are of form `ax + by + cz + d = 0` 
+/*
+The plane paramaters are of form `ax + by + cz + d = 0`
 where `(a,b,c)` is the plane's normal vector and d is the originDist
  */
 typedef struct {