Use JavaScript strict mode, and a few few-character tweaks.

(From #5.)

JavaScript strict mode is useful, if for nothing else than causing an assignment to an undefined/mis-typed variable to raise an error, rather than just creating a new variable under global scope and confusingly continuing in an invalid state. The only change necessary before enabling it was to explicitly attach `ShowBot` to `window`, rather than relying on the implicit global scope.

I also add a few missing semicolons, and a remove pointless use each of `var` and `new`.