Implement hidden nodes blind

[StoneCypher]

NOT READY FOR MERGE

Please merge https://github.com/KnodesCommunity/typedoc-plugins/pull/88 first

Some of this PR is actually from parent patch 88, and will disappear when it is merged

This is a blind attempt to implement HIDDEN nodes. It is highly suspect because the author could not build or test the result, and is new to this codebase.

A HIDDEN node is a node which will only render in the page tree if it's currently being viewed. (This behavior is known to currently be incorrect, and will be repaired before merge once buildable.)

The purpose of a HIDDEN node is to allow a category page to include hundreds of pages underneath, and not flood the index on the right. HIDDEN nodes must be found from a listing in another page, or through search.

My personal use case is for the documentation for a state machine library. I want to include more than 200 example state machines, each on their own page, which is prohibitive without a feature like this.