[Feature request] make wrappers

Inspired by `std::make_tuple` for `std::tuple`..
I recently tried to create 4 simple make methods for types from this library:
```
template
ordered_unique make_ordered_unique(T, M)
{
return {};
}

template
ordered_non_unique make_ordered_non_unique(T, M)
{
return {};
}

template
indexed_by make_indexed_by(T...)
{
return {};
}

template
multi_index_container make_multi_index_container(I)
{
return {};
}
```

These methods allow me to write like this:
```
auto es = make_multi_index_container(make_indexed_by(
make_ordered_unique( tag{}, BOOST_MULTI_INDEX_MEMBER(employee,int,id){}),
make_ordered_non_unique( tag{},BOOST_MULTI_INDEX_MEMBER(employee,std::string,name){}),
make_ordered_non_unique( tag{}, BOOST_MULTI_INDEX_MEMBER(employee,int,age){})));
```

..And the same code without methods (how it works now):
```
typedef multi_index_container<
employee,
indexed_by<
ordered_unique<
tag, BOOST_MULTI_INDEX_MEMBER(employee,int,id)>,
ordered_non_unique<
tag,BOOST_MULTI_INDEX_MEMBER(employee,std::string,name)>,
ordered_non_unique<
tag, BOOST_MULTI_INDEX_MEMBER(employee,int,age)> >
> employee_set;

employee_set es;
```

In my opinion, the variant with make-methods is much better. Why not support for these methods on the library side?