Handling of empty values

[alexejk]

Adding support in decoder to handle empty response values.

As per specification, <struct /> and <array /> are invalid, thus only handling cases below and mapping them to default values:

Value	Default Value
<string/>	""
<int/>, <i4/>	0
<boolean/>	false
<double/>	0.0
<dateTime.iso8601/>	time.Time{}
<base64/>	nil
<array><data/><array>	nil

Fixes #80

[codecov[bot]]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (8c0fd9a) 75.60% compared to head (6fd64e7) 77.52%.

Files	Patch %	Lines
decode.go	91.48%	3 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #81 +/- ## ========================================== + Coverage 75.60% 77.52% +1.92% ========================================== Files 7 7 Lines 541 565 +24 ========================================== + Hits 409 438 +29 + Misses 101 96 -5 Partials 31 31 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
87.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud