This is so that a program like Emacs, which needs only dtoastr,
does not have to bother with distributing and compiling ftoastr
and ldtoastr.
* MODULES.html.sh: Document these modules (ftoastr wasn't documented).
* modules/dtoastr, modules/ldtoastr: New files.
* modules/ftoastr: Now works just for 'float'.
(Files): Remove lib/dtoastr.c, lib/ldtoastr.c.
(Makefile.am): Remove ftoastr.h (not needed and no effect),
dtoastr.c, ldtoastr.c.
