* update and simplify the `load_swc_neuron` reader to match the simplified and more correct interpretation in NEURON 8
* update the documentation on the interpretation, and add details about how it still differs from the neuromorpho descriptions. 
* update unit tests to reflect new interpretation
* add a unit test that reproduces a complex case from the NEURON test suite.
* remove the `load_swc_allen` C++ and Python calls
* add links to NeuroMorpho site in the documention

Fixes #1445.