Cythonized example of LWT interface

[jeromekelleher]

We would like to use the code from @terhorst as an example of using the LWT interface in Cython:

Here is a Cythonized version of one of the C API examples from the docs:

https://github.com/terhorst/tskit_cython_example

Originally posted by @terhorst in #1004 (comment)

[benjeffery]

Awesome, thanks @terhorst. Yes, it would be best to bring this in and test it in CI.

[jeromekelleher]

@terhorst, would you like to copy this in as a PR? It would be good to give you git-credit in the tskit repo for figuring this out! I think a direct copy of what you have into a new directory lwt_interface/cython_example would be ideal. We can hook it up to CI then afterwards.