Some changes
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 * updated diffregr_ex.R & ggmgsa_ex.R
 * diffnet.r: add summary function
 * diffregr.r: add plotting&summary function
 * ggmgsa.R: add mc.flag option in ggmgsa_multisplit;
             ggmgsa_multisplit_par
 * very minor changes in mixglasso.R & nethet.r