define trampoline function
Implement trampoline function, still confusing - really helpful article here http://raganwald.com/2013/03/28/trampolines-in-javascript.html
boilerplate
Asynchronously load all users, run done callback when everything finishes

* Solved loadUsers asynchronously using recursion because the problem
stated not to use while/for loops
* Program sometimes times out
* Official solving version uses .forEach - so I'll rewrite it with it
too 'cause recursive version is slow
Even using .forEach, sometimes solution still times out - so Im leaving both solutions