Progress: Continue implementing controlfile and initfile support.

Progress: Continue implementing controlfile and initfile support.

Fix issue where the `extern` prefix strings accidentally have `_length` in their names.

The entry and rule names should be without their prefixes.
Perform the prefix matching before pulling out the string.
Skip anything that doesn't match the correct prefix when using a loaded file.
Otherwise, operate normally.

This relocates the exit file loading to be at the start, right after loading the entry file.

It may be worth loading all of the rules specified in the entry and the exit at the start.
I added `@todo` and `@fixme` to represent these areas that I need to figure out how I want to handle.