Multithreading Plugin Suite for GBStudio

Three more quality-of-life plugins for GBStudio developers. These will allow you to access GBVM's built-in multithreading capabilities in a way which should be intuitive for beginners to understand. Beware, though, this code is inherently buggy due to data races and technical limitations...don't expect everything to work.

Plugins:

1. Multithread Custom Event
   1. Executes the specified event in a new thread. Only known bug is that variables passed by reference are not modified globally, only locally within the thread. This can create unexpected issues unless handled.
   2. Oh and actors are practically non-functional. Working on it.
2. Wait For Thread
   1. The current script will pause execution until the specified thread has completed. Sometimes, this can cause an infinite loop, resulting in a game freeze. The cause of this bug is currently unknown.
3. Stop Thread
   1. Stops the specified thread.

What is a thread? A thread is a script that runs at the same time as another script. There are two main ways this is accomplished: through hardware (having more CPU cores, which allows each core to run a different script truly simultaneously), or through software (weaving together the instructions for different scripts like a zipper, and executing them all in order, using fast execution time to make it look like they're being executed simultaneously).

Because the GameBoy doesn't have multiple cores (that I'm aware of), multithreading takes the second form. It's slightly slower than hardware multithreading, but just as effective.