add

• lib/towers.lua
• lib/math.lua

math

• dist(x, y, x2, y2) -> distance
• collide2d(x, y, w, h, x2, y2, w2, h2) -> true/false
• torad(degrees) -> radiant

towers

• towers_add(x, y, z, ?model_name)
• towers_draw()