Fix output XML tag order and match ERN XSD definition

[ancorcruz]

Fixes #16

ERN v3.2 XSD defines XML sequences for some elements (enforces elements
order).

DDEX.write generates XML with the elements in the wrong order, for example:

<DisplayArtist>
  <ArtistRole>MainArtist</ArtistRole>
  <PartyName>
    <FullName>Bruno Mars</FullName>
  </PartyName>
</DisplayArtist>

however, the valid XML is:

<DisplayArtist>
  <PartyName>
    <FullName>Bruno Mars</FullName>
  </PartyName>
  <ArtistRole>MainArtist</ArtistRole>
</DisplayArtist>

or

<ImageDetailsByTerritory>
  <TechnicalImageDetails>
    <TechnicalResourceDetailsReference>T12345</TechnicalResourceDetailsReference>
    <ImageCodecType>JPEG</ImageCodecType>
    <ImageHeight>800</ImageHeight>
    <ImageWidth>800</ImageWidth>
    <File>
      <FileName>ABCDEF_T12345.jpg</FileName>
      <FilePath>resources/</FilePath>
      <HashSum>
        <HashSum>aBcDeFgH12345XyZ</HashSum>
        <HashSumAlgorithmType>SHA1</HashSumAlgorithmType>
      </HashSum>
    </File>
  </TechnicalImageDetails>
  <TerritoryCode>Worldwide</TerritoryCode>
</ImageDetailsByTerritory>

while the valid XML is:

<ImageDetailsByTerritory>
  <TerritoryCode>Worldwide</TerritoryCode>
  <TechnicalImageDetails>
    <TechnicalResourceDetailsReference>T12345</TechnicalResourceDetailsReference>
    <ImageCodecType>JPEG</ImageCodecType>
    <ImageHeight>800</ImageHeight>
    <ImageWidth>800</ImageWidth>
    <File>
      <FileName>ABCDEF_T12345.jpg</FileName>
      <FilePath>resources/</FilePath>
      <HashSum>
        <HashSum>aBcDeFgH12345XyZ</HashSum>
        <HashSumAlgorithmType>SHA1</HashSumAlgorithmType>
      </HashSum>
    </File>
  </TechnicalImageDetails>
</ImageDetailsByTerritory>

The root of the issue is in classes that include ROXML and inherit from
another class that also includes ROXML, both defining xml_accessors.

ROXML appends superclass roxml_attrs to the class in use ones, however,
in order to build valid DDEX XML messages we need to list the superclass
attributes before the ones on the child class (as far as I have been able
to check, be aware, the specification is bloated).

Please, check the classes for the previous XML examples:

class DDEX::V20100712::DDEXC::DisplayArtist < DDEX::V20100712::DDEXC::PartyDescriptor
  ...
  xml_accessor :artist_roles, :as => [DDEX::V20100712::DDEXC::ArtistRole], :from => "ArtistRole", :required => false
  ...
end

class DDEX::V20100712::DDEXC::PartyDescriptor < Element
  ...
  xml_accessor :party_names, :as => [DDEX::V20100712::DDEXC::PartyName], :from => "PartyName", :required => false
  ...
end

class DDEX::ERN::V32::ImageDetailsByTerritory < DDEX::V20100712::DDEXC::ImageDetailsByTerritory
  ...
  xml_accessor :technical_image_details, :as => [DDEX::ERN::V32::TechnicalImageDetails], :from => "TechnicalImageDetails", :required => false
  ...
end

class DDEX::V20100712::DDEXC::ImageDetailsByTerritory < Element
  ...
  xml_accessor :excluded_territory_codes, :as => [], :from => "ExcludedTerritoryCode", :required => false
  xml_accessor :territory_codes, :as => [], :from => "TerritoryCode", :required => false
  ...
end

As a solution to this issue, DDEX::Element overwrites ROXML module's class
method roxml_attrs to prepend the superclass attributes instead.

[ancorcruz]

I'm trying to add some specs that probe the issue and also port the patch (tested) to ROXML gem.

[sshaw]

I'm trying to add some specs that probe the issue and also port the patch (tested) to ROXML gem.

Great thanks. Would be a good idea to add a spec that validates output against schema.

[ancorcruz]

that is a really good idea.

Also, I'm going to try and replace test_xml gem with equivalent-xml as it has support to ensure the order of the entities in the document.