PYROMAT: SO2 - ideal gas behavior about pyromat

[chmarti1]

The issue is that PYroMat's SO2 data set is only valid down to 300K, and 25C is outside of that range by 1.85C. The ig2 class SHOULD issue a warning, but it hasn't. Instead, it just returns 0 for enthalpy. You can verify this by typing
SO2.Tlim()
The Tlim() function will return a list with upper and lower temperature limits on the data set in the configured unit system.

[chmarti1]

As a work-around, to FORCE PYroMat to extrapolate down to 25C, you can manually modify the data range inline. You'll be out of the recommended range for these polynomials, but only by 1.85C.

>>> SO2.data['Tlim']
[300.0, 1000.0, 5000.0]
>>> SO2.data['Tlim'][0] = 290.0
>>> so2.h(25)
array([-4633.3206084])

In the next version, I will add out-of-range warnings to the ig2 class. I'll also check to make sure the other classes also handle this error properly (I think do). I will also look to see whether it is worth it to transition to a different coefficient set for some of these ig2 species.