Detect whether there are any 'specials' in a formula term
Expand terms with "||" notation into separate "|" terms
expand double-bar RE notation by splitting
Create list of structures needed for models with random effects
Omit terms separated by vertical bars in a formula
Split formula containing special random effect terms
Substitute safe chars (+) for specials (for use in 'model.frame') (Generalized from 'lme4"s 'subbars' function.)