Fixed path for remarkable.js module
Add get_browser() function

get_browser() function make it possible to identify the current
browser where TiddlyWiki is running, and then it is possible to select
a suitable parsing scheme for math.
First draft of math parsing

Added TeXZilla parsing, which is working for inline and displayed
equations. I think this method is not the best yet, as I still don't
know how to conciliate with MathJax parsing.