Clean up comments

[Lusito]

Currently, a lot of comments exist, which need to be cleaned up.

• [x] If it's a description for a class, method, attribute, etc., convert it to jsdoc syntax and make sure it is up to date for this TypeScript version.
• [x] If it's code that was not commented in original box2d code, implement it (or remove if not needed).
• [x] If it's a comment in original box2d code, keep it?
• [x] If the comment explains something about TypeScript or the specifics to this project, keep it.
  • Except if it's bloody obvious
• [x] Otherwise, remove it.

[Lusito]

Done for the core project. The other projects need a separate look anyway.