add Makefile to .Rbuildignore
add roxygen to Makefile
move typedefs to inst/include/lmresid.h

In Rcpp-dev maillist http://goo.gl/ACYJef , Romain Francois claims that
RcppExports.cpp will automatically include a .h that has the same name
as the package and is located in inst/include
Rcpp attribute will include head file automatically

See the last commit for details
In lmresid.cpp, typedef.hpp to lmresid.h
make -k prebuild should work now
Add eig implementation; rename lmresid to lmresid_lld

Add an implementation using eigen decomposition of symmetric
matrix, which is rank revealing
handle Rd and cpp attribute separately in Makefile
Document() should only update .Rd
A simple introduction in README.md
Add function determinant_cross
Add usage section to README

Also fix some typos
Add document to functions

- lmresid_eig
- lmresid_llt
- determinat_cross