Add support for TradeTax > ExemptionReasonCode

[pableu]

No description provided.

[PATROMO]

@pableu see code style test.

[pableu]

@PATROMO fixed, thanks :)

[PATROMO]

@pableu thanks. Can you extend the Test tests/zugferd211/Tests/BuilderTest.php:169 with your new property?

[pableu]

I can, but I'd have to set it to null or also modify tests/zugferd211/Tests/official_example_xml/zugferd_2p1_XRECHNUNG_Einfach.xml.

The former seems a bit silly, and the latter feels wrong because it's an "official example" and I'd feel bad about modifying it.

Also, anything else than null won't make sense in the context of the sample document because the sample invoice there is including vat, so adding a (Vat)ExemptionReason(Code) other than "null" doesn't make sense.

What do you think? Silly test with null? Or no test?

Or a whole new test? I don't feel confident about adding a completely new test and new test data.

[Lorenzschaef]

@pableu, you can extend the test testBuildXRechnungExtendedExample, which already has more elements than the official example.

[BolZer]

This issue is done with #60. Gonna close this PR.