Use eps instead of zero for temperature check
Add volume to EOS arguments in entropy and enthalpy for the moment

Unify equation of state interface

Continue unifying
Add entropy to debye
Remove __name__==__main block
Add getters for enthalpy and entropy
Add benchmarks for entropy and enthalpy

Remove warning
Merge pull request #67 from ian-r-rose/quasiharmonic_additions

Quasiharmonic additions