Vectors instead of loop iteration; flag 8: direct computation

A) Insstead of looping though data : processing is made in batches
- for each particular value f of flag, we create a subset of all data
based on flag=f, then process the subset in one shot
- where Taylor approximation algorithm is used  (call to uniroot()), we
still use loop iteration over data
- dissociation constants Kxy: for each Kxy, a vector of values for all
data is computed at the beginning in one shot; there is only one call to
function Kxy()

B) for flag=8, approximation of DIC by taylor algorithm is replaced by
direct computation as DIC is linearly dependant on carbonate alkalinity.