Change input,output argument of "pelos.R"

Use matrix format of input argument "observation","coefficient"
  instead of original index form.
Add input argument "structure" to indicate sparsity of "coefficient".
Allow scalar input in "coefficient","initial_value".
Add default input in "coefficient","initial_value".
Add output argument "fitting","residue","rss","observation".
Add "predict.pelos.R"

Currently it can take the returned value from "pelos.R",
  then draw plots of the fitting curves.