Define a set of tags for grouping DFHack tools

[myk002]

We need a bounded set of tags that we can apply to our tools to help users find different "kinds" of tools and to assist in finding related tools. The set does not need to be comprehensive. The online documentation and the DFHack Launcher (#2224) that uses these tags also support full text search that can be used to find things. The tags will just allow us to browse related tools and get more relevant search results.

I think we should target having no fewer than 10 tags and no more than 20, but this can be changed as we dig into this more and come up with more opinions on how it should work.

My first attempt at a taxonomy is here. It may provide some insight, but the "strict categorization" approach it used proved to be inadequate. The categories ended up being arbitrary collections of tools, and a "sub-category" would spring into existence every time a "category" group got too large. This is not an intuitive system for a new reader without prior knowledge of the entire tool set.