Filter option: invert

New filter option: --filter-invert. When present it inverts (negates)
the other filter options combined. This is mostly useful with the -G
option (with -Q the output is limited by the query range (day range)).

The ouput from "calcurse -G <filter options>" is the (set) complement of
"calcurse -G <filter options> --filter-invert". Here <filter options>
may be any combination of filter options.

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/calcurse.h

@@ -427,6 +427,7 @@ enum item_type {
 
 /* Filter settings. */
 struct item_filter {
+	int invert;
 	int type_mask;
 	char *hash;
 	regex_t *regex;