remove Result from the client package

plus make Client interface more consistent. All *Sync functions now
return an error as a second return param. Deliver/Check/Commit use Code
to indicate errors and have IsErr() func defined on ResponseXYZ structs.

types/result.go

@@ -106,6 +106,7 @@ func (r *ResponseCheckTx) Result() Result {
 	}
 }
 
+// IsErr returns true if Code is something other than OK.
 func (r ResponseCheckTx) IsErr() bool {
 	return r.Code != CodeType_OK
 }
@@ -120,6 +121,7 @@ func (r *ResponseDeliverTx) Result() Result {
 	}
 }
 
+// IsErr returns true if Code is something other than OK.
 func (r ResponseDeliverTx) IsErr() bool {
 	return r.Code != CodeType_OK
 }
@@ -145,3 +147,8 @@ func (r *ResponseQuery) Result() *ResultQuery {
 		Log:    r.Log,
 	}
 }
+
+// IsErr returns true if Code is something other than OK.
+func (r ResponseCommit) IsErr() bool {
+	return r.Code != CodeType_OK
+}