VOXELFORMAT: add smoothvoxel support

[mgerhardy]

https://svox.glitch.me/#ModelSyntax https://svox.glitch.me/cheatsheet.html

https://svox.glitch.me/playground.html

size     = 10
scale    = 0.1 0.12 0.1
origin   = -y
clamp = -y
ao = 2 2 // Ambient Occlusion mainly for the top of the trunk

material lighting = flat, roughness = 1, deform =  2, scatter = 0.15
  colors = T:#A20

// Light top and dark bottom foliage with fade for added contrast
// Warp the foliage, regenerate gives a different looking tree every time
material lighting = smooth, roughness = 1, deform =  2, scatter = 0.15, warp = 1 0.2, fade = true
  colors = L:#060 M:#0A0 
voxels
---------- ---------- ---------- ---------- ---------- ---------- ---MMMM--- ---MMMM--- ---------- ----------
---------- ---------- ---------- ---------- ---------- ---LLLL--- --MMMMMM-- --MMMMMM-- ---MMMM--- ----------
------T--- ---------- ---------- ---------- ---LLLL--- --LLLLLL-- -MMMMMMMM- -MMMMMMMM- --MMMMMM-- ---MMMM---
------T--- ---------- ---------- ---------- --LLLLLL-- -LLLLLLLL- MMMMMMMMMM MMMMMMMMMM -MMMMMMMM- --MMMMMM--
-TTTTTT--- ----TT---- ----TT---- ----TT---- --LLLLLL-- -LLLLLLLL- MMMMMMMMMM MMMMMMMMMM -MMMMMMMM- --MMMMMM--
----TT---- ----TT---- ----TT---- ----TT---- --LLLLLL-- -LLLLLLLL- MMMMMMMMMM MMMMMMMMMM -MMMMMMMM- --MMMMMM--
-----T---- ---------- ---------- ---------- --LLLLLL-- -LLLLLLLL- MMMMMMMMMM MMMMMMMMMM -MMMMMMMM- --MMMMMM--
-----T---- ---------- ---------- ---------- ---LLLL--- --LLLLLL-- -MMMMMMMM- -MMMMMMMM- --MMMMMM-- ---MMMM---
---------- ---------- ---------- ---------- ---------- ---LLLL--- --MMMMMM-- --MMMMMM-- ---MMMM--- ----------
---------- ---------- ---------- ---------- ---------- ---------- ---MMMM--- ---MMMM--- ---------- ----------