Adding some new symbols

The goal is to add all the symbols which are mentioned [here](http://en.wikibooks.org/wiki/LaTeX/Mathematics#List_of_Mathematical_Symbols).

This is regarding #53.

I've only added the relational symbols. I'll continue to commit in this branch so __do not merge yet__. I'm sending the pull request early to see if I'm doing anything wrong. So give me some feedback please.