Swap reset() for init(options)

The init method can take an options object, with open tags, closed tags and exposed attributes:

    {
        open: ["div", "p"],
        closed: ["br", "hr"],
        attributes: ["href", "id"]
    }

The init method returns a new tag object, which can be used to overwrite the existing tag object.
Calling init without any arguments, and assigning it to the previous tag object is the new reset().

Since expose() also has to know which tags should be open or closed, it may now also recieve
an options object as its only argument, but this might need to change.