rust mnemonic library added

I'm not affiliated with this implementation but I found it today and it appears to be actively maintained.

Author: lsaether

bip-0039.mediawiki

@@ -156,6 +156,9 @@ JavaScript:
 Ruby:
 * https://github.com/sreekanthgs/bip_mnemonic
 
+Rust:
+ * https://github.com/infincia/bip39-rs
+
 Swift:
 * https://github.com/CikeQiu/CKMnemonic