This is a first implementation of template fields in eXlibris.
Thanks a lot to Alexis (@asalzman) and Nicolas (@nchevaugeon) for fruitful discussions !

Fields can now handle other quantities than double (complex for instance).
This has led to multiple changes:
* xDoubleManager disappears
* xValueDouble disappears
* Assembly is now templatized

However, the changes are small with respect to the interface in your applications (see the testcases).

=========================
    Notable changes
=========================

xDoubleManager:
---------------
Is replaced by  xValueManagerDist<T> ("Dist" stands for "distributed"). This template class handles other values  than double.

Example : xValueManagerDist<double> value_manager;

In your end-user code (AND NOWHERE ELSE), you can define a convenient typedef :
using  xDoubleManager = xValueManagerDist<double>;

xValue:
-------
xValueDouble is replaced by xSingleValue<T> where T stands for the type which is stored.
Move value creat...