[MINOR] correct 'expression' handling

Signed-off-by: etienne <etienne.basset@ensta.org>
[MEDIUM] add a subnet_tool object type('sto') and use it in parse_conversion_specifier
if it is not NULL, it will store the argument it parsed into sto instead of consuming
the va_list *ap

Signed-off-by: etienne <etienne.basset@ensta.org>
[MEDIUM] update match_expr to take a 'sto' arg

Signed-off-by: etienne <etienne.basset@ensta.org>
[MEDIUM] make match expr take a **sto pointer, to store more than one object

Signed-off-by: etienne <etienne.basset@ensta.org>
[BUG] wasnt checking return value of parse_conversion_notifier in match_expr_simple

Signed-off-by: etienne <etienne.basset@ensta.org>
[BUG] SET_ARG didnt set object type

Signed-off-by: etienne <etienne.basset@ensta.org>
[CODING STYLE] remove trailing spaces

Signed-off-by: etienne <etienne.basset@ensta.org>
[CODING STYLE] remove trailing spaces

Signed-off-by: etienne <etienne.basset@ensta.org>
[TYPO] remove trailing spaces

Signed-off-by: etienne <etienne.basset@ensta.org>
[HELPER] consume_valist_from_object

Signed-off-by: etienne <etienne.basset@ensta.org>
[BUG] match_simple should return 0 on no match, even if n chars matches

Signed-off-by: etienne <etienne.basset@ensta.org>