Equations added

This partially addresses issue #321 by adding these equations: ace, enspie, heip_e, fisher_alpha, kempton_taylor_q, mcintosh_e, menhinick, shannon, simpson, and strong. In addition, variable definitions were added to berger_parker_d and to brillouin_d. 
Can you please move the equation and description above, so that it's right below the one-line summary? That way it'll be consistent with the rest of the functions' docstrings.