tag.c: implement '--merged' and '--no-merged' options

Use 'ref-filter' APIs to implement the '--merged' and '--no-merged'
options into 'tag.c'. The '--merged' option lets the user to only list
tags merged into the named commit. The '--no-merged' option lets the
user to only list tags not merged into the named commit.  If no object
is provided it assumes HEAD as the object.

Add documentation and tests for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/tag.c b/builtin/tag.c
index 74eaf25..b2e4ddc 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -23,7 +23,7 @@
 	N_("git tag [-a | -s | -u <key-id>] [-f] [-m <msg> | -F <file>] <tagname> [<head>]"),
 	N_("git tag -d <tagname>..."),
 	N_("git tag -l [-n[<num>]] [--contains <commit>] [--points-at <object>]"
-		"\n\t\t[--format=<format>] [<pattern>...]"),
+		"\n\t\t[--format=<format>] [--[no-]merged [<commit>]] [<pattern>...]"),
 	N_("git tag -v <tagname>..."),
 	NULL
 };
@@ -360,6 +360,8 @@
 		OPT_COLUMN(0, "column", &colopts, N_("show tag list in columns")),
 		OPT_CONTAINS(&filter.with_commit, N_("print only tags that contain the commit")),
 		OPT_WITH(&filter.with_commit, N_("print only tags that contain the commit")),
+		OPT_MERGED(&filter, N_("print only tags that are merged")),
+		OPT_NO_MERGED(&filter, N_("print only tags that are not merged")),
 		OPT_CALLBACK(0 , "sort", sorting_tail, N_("key"),
 			     N_("field name to sort on"), &parse_opt_ref_sorting),
 		{
@@ -418,6 +420,8 @@
 		die(_("--contains option is only allowed with -l."));
 	if (filter.points_at.nr)
 		die(_("--points-at option is only allowed with -l."));
+	if (filter.merge_commit)
+		die(_("--merged and --no-merged option are only allowed with -l"));
 	if (cmdmode == 'd')
 		return for_each_tag_name(argv, delete_tag);
 	if (cmdmode == 'v')