Map stock codes to species names by default in all tables

[cboettig]

As @layamane points out in her review (#46), it probably makes sense for tables to always return species names, since queries are based on species names to begin with.

[cboettig]

All endpoints will return the species name (sciname) in addition to the requested fields (or if no field is included). This should avoid always having to work with speccodes manually.

e.g.

species(common_to_sci("trout"), fields="Vulnerability")

Source: local data frame [9 x 2]

                     sciname Vulnerability
1               Salmo trutta         59.96
2        Oncorhynchus mykiss         36.29
3      Salvelinus fontinalis         43.37
4 Salvelinus alpinus alpinus         74.33
5         Lethrinus miniatus         52.78
6           Salvelinus malma         69.97
7     Plectropomus leopardus         51.04
8  Schizothorax richardsonii         34.78
9          Arripis truttacea         47.96