Make stub files for all unimplemented stdlib modules

If you try to import a module that is in the 2.6 standard library you will now get a not implemented error on import.

All of the files were generated using the script stdlibstubs.py   This doesn't need to be part of the final PR, but you can see how all of these were generated.

This of course increases the size of skulpt-stdlib.js (by roughly 100kb)

Let me know what you think.