Convert documentation to JSDoc

[olleharstedt]

All functions should be documented using JSDoc conventions.

[Lukenickerson]

Naive question: What's the benefit to using JSDoc?

[olleharstedt]

1. Using JSDoc conventions, each argument to functions would be document with @param. Return values would use @return. These conventions are used for PHPDoc and Java, too (and maybe other languages), making it easy to read and get an overview. It's especially useful for dynamically typed language, where the type of an argument might not be obvious (depending on naming conventions etc).
2. JSDoc can generate documentation docs. Not sure if we need that.

[Lukenickerson]

It's google approved (https://google.github.io/styleguide/jsguide.html#jsdoc); I think it's a good idea.