DDSXML11 — Add example of XML data representation for map

7.3.10.4 Data Sample Representation Examples (non-normative) contains examples of how to represent different types of data using XML. Extend those to include maps.

Also, the examples for <aSequenceOfStructs> and <anArrayOfStructs> seem wrong as they only contain a float which does not match any of the defined structures.

Also, the example for <aUnion> does not specify the value of the discriminator which will only work if there is a single discriminator value: It will also not apply to the default case, or if there is no value associated with the discriminator...