2014-05-24  Youyi Fong
    * create package

2014-7-7
    * change the algorithm to use sdc.3.deriv.r in step 2.
    * version shared with Yunda, Allan and Peter

2014-10-7
    * make changes so that x and y and r are understood as to be on the log scale

2014-11-4
    * manuscript submitted
    * changed name from sdc to prc

2014-11-16

2014-11-20
    * make a grid before the loop begins so that the grid point is not
    changing, even though which fall between c and d may be 
    * catch an exception in prc

2014-11-26
    * change optimize interval for sigmasq from 10 fold to 5 fold

2014-11-31
    * fix the estimate of c in both sp and struct to be the TLS estimate of c
    * add a try around call to lm.fit in prcsp
    * use .Call to compute mixlik
