Phase envelope code and data structures set up

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Phase envelope construction working now for Ethane/Propane for a range of mole fractions

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
First step of refactoring of reducing and departure functions

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Finished refactor of reducing parameters at the level of JSON

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Updated generate_headers.py for the new structure of reducing and departure functions

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Refactor of mixing parameters successful

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>