Added enthalpy and entropy for triple point states

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Add docs to describe how to install packages using pip

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

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Added HS skeleton and tests (most fail for now)

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