Extend tfield template parameters with FLDID32

[HerbertKoelman]

Change Tfield template declaration from template< class T > class Tfield to template< class T, FLDID32 F = 0 > class Tfield. This make it possible to declare typedefs of FML fields:

typedef amti::Tfield<std::string,EMPNAME> prenom_t;

prenom_t prenom;
prenom_t chief;

[HerbertKoelman]

This change will impose a change in Tfield declaration syntax.

It's better to move this change into a major release