estream: Support the %b conversion specifier from C23
* src/estream-printf.c (CONSSPEC_BIN): New. (compute_type): Handle it. (parse_format): Support 'b'. (do_format): Divert 'b' to pr_integer. (pr_integer): Print binary format. * tests/t-printf.c (check_fprintf_sf): Add two simple testcases.
Might be handy in some cases and is easy to implement. Minor drawback
is that this increases a stack based buffer from 100 to 150 bytes.