authors: specify maintainers

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

AUTHORS

@@ -1,6 +1,13 @@
-Jason A. Donenfeld <Jason@zx2c4.com>
-Lukas Fleischer <cgit@cryptocrack.de>
-Johan Herland <johan@herland.net>
-Lars Hjemli <hjemli@gmail.com>
-Ferry Huberts <ferry.huberts@pelagic.nl>
-John Keeping <john@keeping.me.uk>
+Maintainer:
+	Jason A. Donenfeld <Jason@zx2c4.com>
+
+Contributors:
+	Jason A. Donenfeld <Jason@zx2c4.com>
+	Lukas Fleischer <cgit@cryptocrack.de>
+	Johan Herland <johan@herland.net>
+	Lars Hjemli <hjemli@gmail.com>
+	Ferry Huberts <ferry.huberts@pelagic.nl>
+	John Keeping <john@keeping.me.uk>
+
+Previous Maintainer:
+	Lars Hjemli <hjemli@gmail.com>