This function calculates mass from time of flight values
based on the following article:
 Titulaer, M. K. and Siccama, I. and Dekker, J. L. and
 van Rijswijk, A. L. and Heeren R. M. and Sillevis Smitt, P. A. and
 Luider, T. M. (2006) 
 “A database application for pre-processing, storage and comparison
 of mass spectra derived from patients and controls”,
 BMC Bioinformatics, 7: 403
 https://pubmed.ncbi.nlm.nih.gov/16953879/
.tof2mass(tof, c1, c2, c3)double, calculated mass
double, vector with times-of-flight
metaData$calibrationConstants[1]
metaData$calibrationConstants[2]
metaData$calibrationConstants[3]
Arguments are imported from metadata (acqu-file).
Titulaer, M. K. and Siccama, I. and Dekker, J. L. and
 van Rijswijk, A. L. and Heeren R. M. and Sillevis Smitt, P. A. and
 Luider, T. M. (2006) 
 “A database application for pre-processing, storage and comparison
 of mass spectra derived from patients and controls”,
 BMC Bioinformatics, 7: 403
 https://pubmed.ncbi.nlm.nih.gov/16953879/