Signal lights around the track
==============================
It is possible to use tracklights in tracks.
Currently, five types of lights are supported (all starting lights):
* red start lights
* green start lights A
* green start lights B
* yellow start lights

All these lights can have an index. I will explain the meaning of these for
every type of light. But first I will give a general example and explain every
option in it:

Example
=======
This example comes from the dirt-3 track.

<section name="Track Lights">
  <section name="1">
    <attstr name="role" val="st_red" />
    <attnum name="index" val="10" />
    <section name="topleft">
      <attnum name="x" val="525.27" />
      <attnum name="y" val="182.68" />
      <attnum name="z" val="20" />
    </section>
    <section name="bottomright">
      <attnum name="x" val="525.27" />
      <attnum name="y" val="181.68" />
      <attnum name="z" val="19" />
    </section>
    <attstr name="texture on" val="data/textures/light-on.rgb" />
    <attstr name="texture off" val="data/textures/light-off.rgb" />
    <attnum name="red" val="1.0" />
    <attnum name="green" val="0.3" />
    <attnum name="blue" val="0.3" />
  </section>
</section>

section "Track Lights": main section
section "1": first lights (lights must be numbered from 1 to the number of
             lights)
attstr "role": the role of the light (see below)
attnum "index": the index of the light (see below)
section "topleft": coordinates of the top-left corner of the light. See remark
                   about coordinates elsewise in this documentation.
section "bottomright": coordinates of the bottom-right corner of the light. See remark
                       about coordinates elsewise in this documentation.
attstr "texture on": texture of the light turned on
attstr "texture off": texture of the light turned off
attnum "red", "gree", "blue": color of the filter to put before the texture.

Coordinate remark
=================
The coordinates can be aquaried from a 3d-editing program. I know an example
where (525,21,-185) was the coordinate in the 3d-program, but (525,185,21) was
the coordinate that was good for the track xml-file. This can be seen by
looking to the axel where the gravity works on: this is the z-axel inside the
game.

Remarks on the different types of lights
========================================

red start lights
----------------
role: st_red
index: index * 0.1s is the time the light is turned on before the start

green start lights A
--------------------
role: st_green
index: ignored
remark: does not go on at the start of a race

green start lights B
--------------------
role: st_green_st
index: ignored
remark: stays on for 30s after the start of the race

yellow start lights
-------------------
role: st_yellow
index: phase (even or odd)
remark: flashes, not used at the moment