Option type checking

[TimothyGu]

As @ForbesLindesay said in #1689, we should probably implement a new error checking system that checks options for type correctness.

[vendethiel]

-1 from me, or at least as an option. I'm not happy with performance butchering again :-).

[ForbesLindesay]

@vendethiel this would have practically zero impact on performance. It only happens on first build of any given template and we're talking about approximately 6 asserts. Totally negligible.

@TimothyGu thanks for adding an issue to track this.

[vendethiel]

Oooh - You mean API options! Not actual attributes. I read that wayy too fast. Sorry, ignore me!