Create a package #69

If this collection of scripts were converted to a package then it might facilitate testing, reuse of code and distribution.

I've been working on a possible route to converting this repo into a package and here is a link to what I'm thinking https://github.com/openmc-data-storage/openmc_data

• Scripts can all become accessible from the command line so they can be run easily from the terminal (partly implemented).
• Testing of that the download urls are still being alive has been partly implemented.
• Testing that each script file exists has been partly implemented
• a single utils file has been made (we use to have two identical files)
• additional shared code has been moved the utils file
• Some more standardisation has been rolled out showing how the deplete scripts could be most similar to the convert scripts (which then allows duplicate code to be removed)

This is a working progress but I wanted to share this idea which brings together a few of the exiting PRs on this data repo. If the idea is welcome then the package can be tidied up and moved over to this org.