mixed effects models

eq_mixed build a formula for multilevel/mixed model

1	eq_mixed(dv, fev, rev, rec, correlated = TRUE, addcons = FALSE)

`dv`	string containing the dependent variable name
`fev`	vector of strings containing variable names for fixed effects
`rev`	list of strings containing variable names for random effects. Each list entry sould be a string vector containing variables combined using the standard operators +,:,* and ^
`rec`	list of strings containing factor variable names for random effects. Each list entry sould be a single string containing factor variables combined using the standard operators +,:,*,^ and /
`correlated`	list of logicals - if TRUE the effects of re variables are modeled as correlated. FALSE is equivalent to the operator \|\|
`addcons`	logical, if TRUE add a constant term to the fixed effects. Overrides 0 and -1 in fev