Replaces custom implementations with existing

This pull request removes the custom implementations of `buffertools.reverse`, `buffertools.toHex` and `buffertools.fromHex` and replaces them with what would already exist.

It is already assumed that if `Buffer` exists in the namespace, that it replicates the Node `Buffer`, therefore, why not use its pre-existing support for hex instead.

Finally, `Array.prototype.reverse` can be applied to any ArrayLike object, so why not use it instead.