Add md5sum

No support for -c at the moment.

md5.h

@@ -0,0 +1,18 @@
+/* public domain md5 implementation based on rfc1321 and libtomcrypt */
+
+struct md5 {
+	uint64_t len;    /* processed message length */
+	uint32_t h[4];   /* hash state */
+	uint8_t buf[64]; /* message block buffer */
+};
+
+enum { MD5_DIGEST_LENGTH = 16 };
+
+/* reset state */
+void md5_init(struct md5 *s);
+/* process message */
+void md5_update(struct md5 *s, const void *m, unsigned long len);
+/* get message digest */
+/* state is ruined after sum, keep a copy if multiple sum is needed */
+/* part of the message might be left in s, zero it if secrecy is needed */
+void md5_sum(struct md5 *s, uint8_t md[MD5_DIGEST_LENGTH]);