[#428] reputation: Define basic types

Define PeerID, TrustValue and Trust types and basic methods on them.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/reputation/peer.go

@@ -0,0 +1,17 @@
+package reputation
+
+const peerIDLength = 33
+
+// PeerID represents identifier of reputation system participant.
+type PeerID [peerIDLength]byte
+
+// Bytes converts PeerID to []byte.
+func (id PeerID) Bytes() []byte {
+	return id[:]
+}
+
+// PeerIDFromBytes restores PeerID from []byte.
+func PeerIDFromBytes(data []byte) (id PeerID) {
+	copy(id[:], data)
+	return
+}