Class Alert doesn't store any provided information

[Byloth]

As briefly described in the Issue #9, Vuert allows the developer to extend the options provided (among the default ones) when emitting a new alert.
Or, at least, it should do so... In reality, it isn't like that.

In the constructor of the Alert class, the options are -indeed- selected one by one and assigned to the Alert object.
What happens if the developer adds some new properties? They're simply ignored and lost.

Should it just use the payload property that accepts any kind of data?
What if I want to provide some data to the AlertHandler but not to any eventual custom child component?