Solid RX core refactored

This is a refactored version of the core of Solid's reactive system. I made it for learning the codebase myself, but thought it might be useful for others. This version has documentation, as well as a lot of small refactorings like different variable names, however it's still equivalent to the original code. This codebase includes some the functions from Solid's signal.ts file. All of the code for suspense and scheduling was removed from inside the functions, the same as Rollup will do if you don't use those features. I also removed all dev mode and error handling code.