include BP calculations in transformed parameters block, improve declaration...

include BP calculations in transformed parameters block, improve declaration for better understanding and include flexibility for BP parameters prior specification; details below:

1 - replace p by q to denote the nº of features in data block 2 - replcace dist by rand to denote the type of frailty 3 - replace b and B by g and G to denote BP basis 4 - replace priorpars by par1_gamma and par2_gamma- now vector of size m (one for each gamma) 5 - replace priordist by priordist_gamma- now vector of size m 6 - replace beta_scaled and gamma_scaled by gamma_star and beta_star

all of the above changes are intended to make the program more mnemonic in accordance with arXiv:2003.10548

7 - omit standartization of the transformed effect beta_star 8 - include loop for BP basis in the transformed parameters block, excerpt withdrawn from the loglik_aft function in loglikbp.stan

9 - update arguments of loglik functions in loglikbp.stan 10 - include a for loop to accomodate prior selection for each BP parameter