Allow passing arbitrary options to KaTeX

[ibrahima]

https://github.com/Khan/KaTeX#rendering-options

Personally, I wanted to set the maxSize option to KaTeX, but I figured that there are a lot of other options to KaTeX that a user might want to pass in, and it would be tedious to try to keep this component in sync with any options that KaTeX adds. So I thought this would be a good approach.

We could also use PropTypes.shape and specify the currently known KaTeX options, and that way if any new options are added a user can still pass them in via an object, and the worst case is that they get a warning from PropTypes.

Let me know what you think. Thanks!