add code documentation

[katjaq]

MicroDraw uses docjs – without any installation this will output code comments into a documentation of all the functions.
For this to work, we have to put comments in the following style before every single function

/**
 * @function nameOfTheFunction
 * @desc Description of what the function does.
 * @param {type} varName Description of the variable that the function takes as input argument.
 * @returns {type} What the function returns.
 */

and here starts the function

type can be things like {object} or {string} or {number} or {boolean}

We have already put some comments into the code, but there are far more to go! :)

The code documentation is then immediately updating from the inserted comments and visible at
http://localhost:3000/doc/code.html