* separator can cause issue when sending data (WebService, FSD)
* re-parsing (print and parse again) can cause to undesired results as the separator is mistaken as decimal separator with a different locale
* separator now a parameter so it can still be used
* All members of CMeasurementUnit moved into nested pimpl class Data.
* CMeasurementUnit has only one member: a pointer to a const Data.
* Static const CMeasurementUnits replaced with static const Datas.
* Each CMeasurementUnit singleton method returns by-value a CMeasurementUnit containing a pointer to a static const Data.
* Means CMeasurementUnit is trivial to copy because we never copy the pimpl members.
** Works because the available units are fixed at compile time so we never need to create novel units at runtime.
