calculates percent mass breakdowns for formulas
thanks to https://github.com/Bowserinator/Periodic-Table-JSON :)
$ node percentMass.js H Cl
Total Mass of H1Cl1: 36.458000000000006g/mol
% Mass for H: 0.02764825278402545
% Mass for Cl: 0.9723517472159745
$ node percentMass.js K Mn O4
Total Mass of K1Mn1O4: 158.0323543g/mol
% Mass for K: 0.24740699569518465
% Mass for Mn: 0.34763795390726515
% Mass for O: 0.40495505039755014
**Mg(NO3)2 is written as Mg(1) N2 O6**
$ node percentMass.js Mg N2 O6
Total Mass of Mg1N2O6: 148.313g/mol
% Mass for Mg: 0.1638763965397504
% Mass for N: 0.18888431897406163
% Mass for O: 0.6472392844861881
**(NH4)3PO4 is written as N3 H12 P(1) O4**
$ node percentMass.js N3 H12 P O4
Total Mass of N3H12P1O4: 149.0867619985g/mol
% Mass for N: 0.28185601080009226
% Mass for H: 0.08113396412836238
% Mass for P: 0.20775662160273917
% Mass for O: 0.42925340346880614