Lapack tests now use c++-based calls

 - not working in reduced-rank case
Cosmetic changes to lin regr tests
Fixed the bug in calc_rss_lapack
Remove the C-based lapack routines as c++ version works

 - Also update the vignette
Add header file for linreg_lapack.cpp
Don't seem to need Makevars file, nor to include Applic.h