using the struct-scheme.hpp and the requirements for
EntryID as a guideline. The goal is to move EntryID
over into the support lib, which means we need to get rid
of all direct proc::asset dependencies. Thus, these generic
ID functions shall form a baseline implementation, while
asset::Struct may provide the previously used implementation
through specialisation -- so the behaviour of EntryID will
not change for the structural assets, but we'll get a more
sane and readable default implementation for all other types.
still puzzled why this instantiation of MultiFact fails to compile with GCC 4.8
so I'm bound to understand why the types involved
need indeed to be are structured the way they are right now.
previous versions used to resolve this ambiguity in favour of a ctor call,
but now the compiler treats such constructs as function definition;
this is reasonable, since C++11 introduced the notion of a "generalised
initialisation", which is always written as a (possibly empty) list
in braces.
In these specific cases here, we just omit the empty parens
