httk 2.3.1 (2023-3-19)

This patch addresses a number of bugs.

Bug Fixes

Argument keepit100 was being improperly ignored by get_fabsgut
Fixed issue where create_mc_samples could not handle argument
parameters being a list (as in,
parameters=parameterize_steadstate(chem.name="bisphenola"))
Error messages for calc_css now explain that function is only applicable
to dynamical (time-evolving) models and handles errors with other models
(such as 3compartmentss) more gracefully
Changed Rblood2plasma to Rfblood2plasma for fetal plasma in model fetal_pbtk
(Thank you to Kimberly Troung)
Liquid densities previous referred to as ppmv for convert_units were
actually ppmw. Cannot calculate ppmv without chemical-specific liquid density,
which we do not know.
Added model descriptor compartment.state to indicate which compartments are
liquid and which are gaseous

Changed armitage_eval to allow chemical specification by usual arguments
chem.name, chem.cas, and DTXSID. Preserved casrn.vector for backward compatibility.
Changed armitage_eval to allow multiple instances of chemicals (no longer
using CASRN as row names) -- thank you Katie Paul Friedman for suggestion
Added Katie Paul Friedman (USEPA) as contributor for long history of
suggesting refinements and putting up with bugs
Function solve_model now gives warnings when ignoring elements of
dosing for a given model and route (acceptible dosing.params are now
specified by the modelinfo_[MODEL].R file)