Overhaul node_data organization

[tdene]

node_data is currently stored across multiple files in a separate folder.

#103 raises the point that users of this library need to be able to side-load custom node_data for their own purposes, as opposed to being forced to fork the library and edit the node_data folder.

This has been implemented by #105 in a quick manner. This is sufficient for now.

However, the node_data organizational style must be re-thought. There are several other references throughout the code to the need for a re-invention of node_data.

And now, with #105 in mind, surely a better delivery format can be considered. That is to say, if this library is to prioritize side-loading of node_data for possible users, it should make that the main form in which node_data is delivered. There should be no temptation for users to fork this repository and add in new files, but rather the base repository should dedicate itself fully to a single way of providing node_data that is compatible with side-loading and can serve as a tutorial for it.