fixed8: remove trailing zeroes from string representation

Add some testcases from `dev` branch (with less than zero case added) and
remove useless trailing zeroes from the resulting string.

pkg/rpc/server_test.go

@@ -165,7 +165,7 @@ var testRpcCases = []tc{
 	{
 		rpcCall:        `{ "jsonrpc": "2.0", "id": 1, "method": "getaccountstate", "params": ["AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y"] }`,
 		method:         "getaccountstate_1",
-		expectedResult: `{"jsonrpc":"2.0","result":{"version":0,"script_hash":"0xe9eed8dc39332032dc22e5d6e86332c50327ba23","frozen":false,"votes":[],"balances":[{"asset":"0x602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7","value":"72099.99960000"},{"asset":"0xc56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c9b","value":"99989900"}]},"id":1}`,
+		expectedResult: `{"jsonrpc":"2.0","result":{"version":0,"script_hash":"0xe9eed8dc39332032dc22e5d6e86332c50327ba23","frozen":false,"votes":[],"balances":[{"asset":"0x602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7","value":"72099.9996"},{"asset":"0xc56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c9b","value":"99989900"}]},"id":1}`,
 	},
 
 	// Bad case, invalid address

pkg/util/fixed8.go

@@ -34,7 +34,7 @@ func (f Fixed8) String() string {
 		for i := len(str); i < 8; i++ {
 			buf.WriteRune('0')
 		}
-		buf.WriteString(str)
+		buf.WriteString(strings.TrimRight(str, "0"))
 	}
 	return buf.String()
 }

pkg/util/fixed8_test.go

@@ -19,7 +19,7 @@ func TestNewFixed8(t *testing.T) {
 
 func TestFixed8DecodeString(t *testing.T) {
 	// Fixed8DecodeString works correctly with integers
-	ivalues := []string{"9000", "100000000", "5", "10945"}
+	ivalues := []string{"9000", "100000000", "5", "10945", "20.45", "0.00000001", "-42"}
 	for _, val := range ivalues {
 		n, err := Fixed8DecodeString(val)
 		assert.Nil(t, err)