Alternative Prey Values To Include in Package That May Be Useful for Users

[sborstein]

Fairly self explanatory. Right now we include FishBase prey values and plan to implement the values for sharks from Cortes, 1999, but there may be additional one users may want to include.

[sborstein]

Possibly add dataset used in paper and implement it in vignette

[sborstein]

Dataset used in paper is in package and vignette as Herichthys. Other possible prey values people may want would be easy to add.