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. 
`P_i` should be lowercase (i.e., `p_i`) to be consistent with the `dominance` equation. `5` should be changed to `s`, where `s` is the number of OTUs.