[VEX] get bbox

------- getbbox
void  getbbox(<geometry>geometry, vector &min, vector &max)
void  getbbox(<geometry>geometry, string primgroup, vector &min, vector &max)
void  getbbox(vector &min, vector &max)
------- getbbox_center
------- getbbox_max

------- getbbox_min
------- getbbox_size
vector  getbbox_size(<geometry>geometry)
vector  getbbox_size(<geometry>geometry, string primgroup)
ex).
------- getbounds
------- getpointbbox

------- getpointbbox_center
vector  getpointbbox_center(<geometry>geometry)
vector  getpointbbox_center(<geometry>geometry, string pointgroup)
ex).
------- getpointbbox_max
------- getpointbbox_min
------- getpointbbox_size
------- relbbox
------- relpointbbox
------- texture3dBox