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. 
``:math:`gamma^2_{ace}``` isn't rendering correctly (the word *gamma* is displayed instead of the symbol). I think you need to precede *gamma* with two backslashes.