output formamide corrected delta G, vary delta G based on hybridization temperature

[jil24]

For delta-G based formamide correction, it would be nice to output a corrected delta G. Currently only the Tm output changes.

Similarly, it looks like the delta G calculations are hardcoded for a hybridization temperature of 37 C. This is sometimes useful to vary if you're looking for probes with different Tm but the same delta G at a given temperature