update documentation.
remove the unnecessary print statements.
simu_zhouandli2016.add simulation setup used in paper, including
simu_factor_model_paras and simu_factor_model_data.simu_reg_coefs and simu_reg_data.add tuning strategy proposed in paper (tune_drrglm and tune_drr_factor_model).
add EEG data (~7MB) used in real data analysis.
mathjaxr, use the built-in macros for math expression in documentation (supported since R-4.2.2)