Update: Adding missing thread functions and types; restructure files.

Update: Adding missing thread functions and types; restructure files.

It has become clear to me that I didn't actual complete the thread types.
This adds the array of array types that are missing.

The `thread.c` and `thread.h` files are huge.
Break apart the functions based on existing `thread/*` files.
Doing this requires being more particular about the ordering of the header includes.

Update and add appropriate unit tests.

Much of this is done via mass replacements.
There very likely are some unimportant oversights.