mixing: add mixclient package

The mixclient package implements a client for the peer-to-peer mixing process.
It depends on a mixpool to send and receive mixing messages to and from the
network.

mixing/mixclient/blame.go

@@ -0,0 +1,18 @@
+package mixclient
+
+// blamedIdentities identifies detected misbehaving peers.
+//
+// If a run returns a blamedIdentities error, these peers are immediately
+// excluded and the next run is started.
+//
+// If a run errors but blame requires revealing secrets and blame assignment,
+// a blamedIdentities error will be returned by the blame function.
+type blamedIdentities []identity
+
+func (e blamedIdentities) Error() string {
+	return "blamed assigned"
+}
+
+func (e blamedIdentities) blamed() []identity {
+	return ([]identity)(e)
+}