endf2ncmat could use endf-parserpy

[marquezj]

The library endf-parserpy is a suitable alternative for pyne in endf2ncmat, and it is more likely to keep up with the changes of the ENDF-6 format. Currently it can be installed using pip, but it would be an optional requirement.

I have been using for creating ENDF-6 files (#183) and it is a nice package.

I can work on modifying endf2ncmat to use endf-parserpy and create a pull request, unless you have other plans for the script.