Add inline documentation

[o-alexandre-felipe]

I use InteliJ webstorm (free propaganda here), and it is convenient when the code has inline documentation.

First I noticed that the return type was not defined in the module declarations.

Looking into the implementation I concluded that it must return a number .

I also changed the return type of the comparison function (that by the way I extracted in a separate interface). The previous declaration accepts null or undefined as return types. I think that this would lead to some confusion, e.g. bounds.lt(array, y) + 1 != bounds.ge(array, y), in an array where y appears multiple times.

The screenshot shows how the inline documentation appears in the IDE