GLMM_MCMC function.
  Besides initial (RE)ML fits, the function created variables
  derived from the design matrices.THIS FUNCTION IS NOT TO BE CALLED BY ORDINARY USERS.
GLMM_MCMCifit(do.init, na.complete,
    y, dist, id, time, x, z, random.intercept,
    xempty, zempty, Rc, Rd, p, p_fi, q, q_ri, lalpha, dimb)TRUE then
    the function removes rows containing NA's from y, id, x,
    z whenever there is at least one missing value for arbitrary
    response. If FALSE y of GLMM_MCMCdata
    functiondist of GLMM_MCMC
    functionid of GLMM_MCMCdata
    functiontime of GLMM_longitClustx of GLMM_MCMCdata
    functionz of GLMM_MCMCdata
    functionrandom.intercept of GLMM_MCMCdata
    functionxempty of GLMM_MCMCdata
    functionzempty of GLMM_MCMCdata
    functionRc of GLMM_MCMCdata
    functionRd of GLMM_MCMCdata
    functionp of GLMM_MCMCdata
    functionp_fi of GLMM_MCMCdata
    functionq of GLMM_MCMCdata
    functionq_ri of GLMM_MCMCdata
    functionlalpha of GLMM_MCMCdata
    functiondimb of GLMM_MCMCdata
    functiondo.init is FALSE):time upon removal of missing valuesGLMM_MCMC.