Link element order and priority tests

[iherman]

The PR adds two tests to the link element in §5.3 of the reading system spec, for the following statement:

When resolving discrepancies and conflicts between metadata expressed in the package document and in linked metadata records, reading systems MUST use the document order of link elements [epub-33] in the package document to establish precedence

Fix #171

@m22chan, I reused an older test of yours (I have added a small sentence into the description, b.t.w.) with minimal changes, so I kept your name. I look at the onix file would be helpful to be sure that the title I added is o.k.

[m22chan]

@iherman Ahh, okay, I see.
Since the two ONIX files in your additional test are in ONIX 3.0 format, I think we might have to move that title data down under the <TitleDetail>. We might also need to update the name of the element to match how Editeur renamed those fields when they went to version 3.0 of ONIX.

So for sampleONIX-30-first.xml, like:

<?xml version="1.0"?>
<ONIXMessage xmlns="http://ns.editeur.org/onix/3.0/reference" release="3.0">

  <Header>
    <Sender>
      <SenderName>My Publishing Company or Client Services Provider</SenderName>
    </Sender>
    <SentDateTime>20150723T142048Z</SentDateTime>
  </Header>

  <Product>
    <RecordReference>9789999999991</RecordReference>
    <NotificationType>04</NotificationType>

    <ProductIdentifier>
      <ProductIDType>15</ProductIDType>
      <IDValue>9789999999991</IDValue>
    </ProductIdentifier>

    <DescriptiveDetail>
      <ProductComposition>00</ProductComposition>
      <ProductForm>ED</ProductForm>

      <TitleDetail>
        <TitleType>01</TitleType>
        <TitleElement>
          <TitleElementLevel>01</TitleElementLevel>
          <TitleText>ONIX metadata title (first)!</TitleText>
        </TitleElement>
      </TitleDetail>
      <Language>
        <LanguageRole>01</LanguageRole>
        <LanguageCode>eng</LanguageCode>
      </Language>
      <Extent>
        <ExtentType>10</ExtentType>
        <ExtentValue>1234</ExtentValue>
        <ExtentUnit>03</ExtentUnit>
      </Extent>
    </DescriptiveDetail>

The rest of the file would be unchanged so I won't paste it here.

Similarly, for sampleONIX-30-second.xml:

<?xml version="1.0"?>
<ONIXMessage xmlns="http://ns.editeur.org/onix/3.0/reference" release="3.0">

  <Header>
    <Sender>
      <SenderName>My Publishing Company or Client Services Provider</SenderName>
    </Sender>
    <SentDateTime>20150723T142048Z</SentDateTime>
  </Header>

  <Product>
    <RecordReference>9789999999991</RecordReference>
    <NotificationType>04</NotificationType>

    <ProductIdentifier>
      <ProductIDType>15</ProductIDType>
      <IDValue>9789999999991</IDValue>
    </ProductIdentifier>

    <DescriptiveDetail>
      <ProductComposition>00</ProductComposition>
      <ProductForm>ED</ProductForm>

      <TitleDetail>
        <TitleType>01</TitleType>
        <TitleElement>
          <TitleElementLevel>01</TitleElementLevel>
          <TitleText>ONIX metadata title (second)!</TitleText>
        </TitleElement>
      </TitleDetail>
      <Language>
        <LanguageRole>01</LanguageRole>
        <LanguageCode>eng</LanguageCode>
      </Language>
      <Extent>
        <ExtentType>10</ExtentType>
        <ExtentValue>1234</ExtentValue>
        <ExtentUnit>03</ExtentUnit>
      </Extent>
    </DescriptiveDetail>

[iherman]

Thanks a lot, @m22chan ! I have updated all ONIX files accordingly.

If otherwise you think the tests are o.k., can you approve the PR?

Thanks again

[m22chan]

Looks good!