Cleanup of OptionStrategy

[lukasz-pyrzyk]

I spent a couple of minutes to find out that i cannot use OptionAttribute with types different than bool. That is why I've added helpful information for another people.

Also, i did some general cleanup of whole class.

[Nick-Lucas]

Hey Lukasz,

Thanks a lot for sending this in, your updated exception message is a really great change.

Unfortunately I won't be able to merge this in, because of the style changes, which no longer match the style used throughout this project.

However, I'm currently planning a round of changes to improve exception messages and make some bad-scenarios clearer to both developers and users, so will definitely bring over your change when I do this.
Of course if you want to slim down the PR to just the message improvement, I'll happily merge this in for you.

Nick :)

[lukasz-pyrzyk]

Hi.

Sure, if you are going to improve exception messages i think my change is redundant :)

Thanks