[WIP][refactor] Attach methods to prototype instead of object.

[cirosantilli]

Doing:

• @func = -> inside of the constructor attaches methods to objects, which uses extra memory if there are multiple objects
• func: -> attaches to .prototype, so one per class.

Since it is more efficient, it is also more common, and therefore easier to identify the instance methods.

Also requires using @user instead of _user closure variable, which is good as it makes it clear what is an instance variable and what is a local one.

If good I will do this for every class.

Only the 2 currently failing tests fail like before this PR.