Improve Docs

[rwnx]

Now that we're publishing docs over at https://rwnx.github.io/hardwire/ I think we should reformat and document with this in mind.

Suggestions/Improvements:

• The top level modules don't make it clear what the Root namespace is for (it's for documentation!)
• Some of the methods don't give clear examples or expected usage
• Some of the internal workings should be hidden (e.g. REGISTRATIONS should probably be considered private)