Added four mathjax equations in the docstrings: berger_parker_d, brillou...

...in_d, margalef and mcintosh_d.
Ok, I think it may be an issue with your text editor. I think I'll pull this and clean up myself (might be easier at this point). What text editor are you using? If you're not heavily invested in it, I think you should using [Atom](https://atom.io/) for your coding.