some functions had vague names, I even ended up re-writing some of these functions by accident!
also added doxy comments.
* ED_view3d_win_to_3d (was window_to_3d)
* ED_view3d_win_to_delta (was window_to_3d_delta)
* ED_view3d_win_to_vector (was window_to_3d_vector / viewvector)
* ED_view3d_win_to_segment_clip (was viewline)
* ED_view3d_win_to_ray (was viewray)