add hash proc to support using with containers (#516)

libp2p/cid.nim

@@ -11,7 +11,7 @@
 
 {.push raises: [Defect].}
 
-import tables
+import tables, hashes
 import multibase, multicodec, multihash, vbuffer, varint
 import stew/[base58, results]
 
@@ -268,6 +268,9 @@ proc encode*(mbtype: typedesc[MultiBase], encoding: string,
   ## ``encoding``.
   result = MultiBase.encode(encoding, cid.data.buffer).tryGet()
 
+proc hash*(cid: Cid): Hash {.inline.} =
+  hash(cid.data.buffer)
+
 proc `$`*(cid: Cid): string =
   ## Return official string representation of content identifier ``cid``.
   if cid.cidver == CIDv0: