Env player surface trigger

It monitors the  of the material of the surface the player is standing on, and fires outputs whenever it changes to/from a specific material.

Keyvalues

 * {| class=tbl

! Literal value || Description
 * 0 || None (player is in the air)
 * 67 || Concrete
 * 77 || Metal
 * 68 || Dirt
 * 86 || Vent
 * 71 || Grate
 * 84 || Tile
 * 83 || Slosh (Surfaceprop must be "water" or "slime". Does not detect actual water.)
 * 87 || Wood
 * 80 || Computer
 * 89 || Glass
 * 70 || Flesh
 * 73 || Clip
 * 79 || Foliage
 * 78 || Sand
 * }
 * 87 || Wood
 * 80 || Computer
 * 89 || Glass
 * 70 || Flesh
 * 73 || Clip
 * 79 || Foliage
 * 78 || Sand
 * }
 * 73 || Clip
 * 79 || Foliage
 * 78 || Sand
 * }
 * 78 || Sand
 * }
 * }