Multiple Tri Layer support

[pcasotti]

Currently we only support one Tri Layer:

[behavior]
tri_layer = { upper = 1, lower = 2, adjust = 3 }

The idea is to add support for multiple:

[behavior]
tri_layers = [
    { upper = 1, lower = 2, adjust = 3 },
    { upper = 4, lower = 5, adjust = 6 }
]