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.

filters/owner-example.lua

@@ -0,0 +1,17 @@
+-- This script is an example of an owner-filter.  It replaces the
+-- usual query link with one to a fictional homepage.  This script may
+-- be used with the owner-filter or repo.owner-filter settings in
+-- cgitrc with the `lua:` prefix.
+
+function filter_open()
+	buffer = ""
+end
+
+function filter_close()
+	html(string.format("<a href=\"%s\">%s</a>", "http://wiki.example.com/about/" .. buffer, buffer))
+	return 0
+end
+
+function filter_write(str)
+	buffer = buffer .. str
+end