Adds capability for RedlichKwongMFTP to read a database of critical properties
for Tc and Pc of common species, so that users do not need to input pureFluidParameters
for every single species, thereby reducing burden during creation of new cti files.

For any species where pureFluidParameters are not provided by the user, function
getCoeffs scans the database looking for matches.  Any unmatched species will throw
an error.  Currently only scans by species name string, and is only intended for
common species with well-known critical properties.

Current operation is quite slow if the table is consulted for a large number of
species.  In the future, should also implement the capability to write the updated
pureFluidParameters back into the xml file, so the user only has to perform the lookup
once.