Function: nfsubfieldsmax
Section: number_fields
C-Name: nfsubfieldsmax
Prototype: GD0,L,
Help: nfsubfieldsmax(nf,{flag=0}): computes the list of maximal subfields of
 nf. The result is as in nfsubfields.
Doc: Computes the list of maximal subfields of \var{nf}. The result is a vector
 as in \tet{nfsubfields}.

 An input of the form~\kbd{[nf, fa]} is also allowed, where~\kbd{fa} is the
 factorisation of~\var{nf.pol} over~\var{nf}, and~\var{nf} is also allowed to
 be a monic defining polynomial for the number field.
