Allow specifying temperature

[Aariq]

Would close #41

Additions

• Hook up temp_k arg to calc_vol() (or use ºC and call it temp_c)
• Warn users if temperature is extrapolating beyond range (0-120ºC) OR potentially error unless extrapolate = TRUE
• Extend temperature specification to work with meredith method
• Clarify in documentation how meredith method works (which SIMPOL.1 coefs are being used for additional groups)
• Add sentence in documentation about how accuracy changes with temperature in SIMPOL.1

Bug fix:

• You can now use named vectors for SMILES input and the names are used as the chemical names.