I'm having some trouble processing big 3d volumes using the library. The cause seems to be a lack of bounds checking on buf access in fill() and trace(), buf being statically sized. Due to the numba.jit usage it manifests as a segfault due to the out-of-bounds write.

Here's a PR to add that bounds checking, and allows caller specification of the fixed buffer size to build_sknw():
#2

I guess it could also be dynamically resized, but I'm not familiar with numba.jit flavoured python so I'll leave that.