Anisotropy in theta needs adaptation of define_line_splitting()

[mknaranja]

If we allow anisotropy in theta (which basically should be possible) but was never really used due to our use cases, we have to adapt:

https://github.com/mknaranja/GMGPolar/blob/main/src/smoother.cpp#L79

Further, when we calculate "delete circles" in level::define_line_splitting() (smoother.cpp line 73), we use that the grid spacing in theta is constant, dont we ? If anisotrophy is chosen in theta I think one should update that function as well!

Originally posted by @CodingAllan in #37 (comment)