compilation in tox virtualenv works

bfps/cpp/spline_n1.hpp

bfps/cpp/spline_n2.cpp

bfps/cpp/spline_n2.hpp

bfps/cpp/spline_n3.cpp

bfps/cpp/spline_n3.hpp

bfps/cpp/tracers.cpp

bfps/cpp/tracers.hpp

bfps/cpp/vector_field.cpp

bfps/cpp/vector_field.hpp

setup.py

tox.ini