Minor change to the Makefile:
The Makefile is only needed for testing FLENS-LAPACK with Netlib's Lapack Testsuites. Building the Lapack test suites requires a Fortran compiler.
However, most user just want to use FLENS and therefore do not need that. Just include FLENS to your compile command, e.g.
g++ -Wall -std=c++11 -I /Users/lehn/work/FLENS tut01-page01-example.cc
FLENS is a header-only C++ library. So installing FLENS means simply copying it to a place it is accessible.