Bug: infinite loop in TemplateParser

[wiktoriak777]

The parser runs into an infinite loop when parsing this article: https://de.wikipedia.org/wiki/Elliptische_Koordinaten. I've come to the conclusion that the problem is caused by the occurence of {{ inside of LaTeX math expressions. It seems to be related to the comment in info.bliki.wiki.filter.TemplateParser referring to issue #153. Adding the case for the <math> tag back in solves the infinite loop problem.

I would appreciate it if somebody else took a look at this.