Add ability to use non-standard species to `psdCalc()`

[droglenc]

Per request from Nick Heredia ... add ability to use psdCalc() with a species that does not exist in psdLit.

This should be a fairly quick addition ... just bypass call to psdVals() early in psdCalc() and make some catches if the user does not send the full compliment of length (i.e., one for each length category).