Rename disableTLD option to removeSubdomains

In #9, @chriszarate has suggested that the option name `disableTLD` is imperfect.
I agree. We can still change the name, but what should it be?

After long consideration I came up with `removeSubdomains`.
I think a long time ago the bookmarklet had a similar wording as well.

This wording more clearly explains its behavior.
In addition, negative options lead to double negatives in setting the option,
which is significantly more confusing than positives.

What do you think?