Options: use the new 'output' option of Katex (>= v0.11.0)

[schullq]

Hello,

I'm using ng-katex on a little project I'm doing for fun. Very useful.

I realized that the options of ng-katex does not implement the 'output' options, newly introduced since Katex v.0.11.0. By default, Katex is rendering both in the same string.

I think it would be nice to have it, and avoid having the MathML and the HTML version printed every time.

[garciparedes]

Hi @schullq!

It's an interesting change, I'll merge your pull request. 🙂