CData -> CDATA

[KronosTheLate]

From https://www.w3.org/TR/xml/:

The spec seems to show only CDATA in all caps. The issue is of course that this package writes "CData", with the last 3 letters lowercase. I noticed this when working on a GPX file, and this GPX validator shows an error when CDATA is not in all caps for the following XML content:

  <?xml version="1.0"?>
<gpx version="1.1" creator="CoMaps" xmlns="http://www.topografix.com/GPX/1/1" xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3" xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 https://www.topografix.com/GPX/1/1/gpx.xsd http://www.topografix.com/GPX/gpx_style/0/2 https://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 https://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd">
  <metadata>
    <name>Bookmarks</name>
  </metadata>
<wpt lat="23.966643" lon="55.736415">
    <name>My Tag Name</name>
    <desc>
      <![CData[R&B]]>
    </desc>
</wpt>
</gpx>

To fix this, this PR replaces <![CData[ with <![CDATA[ in all files in this package. It does not change the capitalization of the types themselves, which should of course follow the julia convention.