Long time coming, convert R to method taking mole fractions (sigh...)

include/teqp/algorithms/VLE.hpp

include/teqp/algorithms/critical_tracing.hpp

include/teqp/constants.hpp

include/teqp/derivs.hpp

include/teqp/models/CPA.hpp

include/teqp/models/eos.hpp

include/teqp/models/multifluid.hpp

include/teqp/models/pcsaft.hpp

src/main.cpp

src/teqp_profile.cpp

src/tests/catch_tests.cxx