repolist: add owner-filter

This allows custom links to be used for repository owners by
configuring a filter to be applied in the "Owner" column in the
repository list.

cgit.h

@@ -57,7 +57,7 @@ typedef enum {
 } diff_type;
 
 typedef enum {
-	ABOUT, COMMIT, SOURCE, EMAIL, AUTH
+	ABOUT, COMMIT, SOURCE, EMAIL, AUTH, OWNER
 } filter_type;
 
 struct cgit_filter {
@@ -104,6 +104,7 @@ struct cgit_repo {
 	struct cgit_filter *commit_filter;
 	struct cgit_filter *source_filter;
 	struct cgit_filter *email_filter;
+	struct cgit_filter *owner_filter;
 	struct string_list submodules;
 };
 
@@ -257,6 +258,7 @@ struct cgit_config {
 	struct cgit_filter *commit_filter;
 	struct cgit_filter *source_filter;
 	struct cgit_filter *email_filter;
+	struct cgit_filter *owner_filter;
 	struct cgit_filter *auth_filter;
 };