XTCE12 — XTCE issue - add shortDescription to EntryList entries

Items in entryList should each have their own optional shortDescription attribute for documentation at each entry of the container itself.

Items in entryList should each have their own optional shortDescription attribute for documentation at each entry of the container itself.

Add an optional shortDescription attribute to the SequenceEntryType. As an optional description, it will not affect the upward (1.1 to 1.2) interpretation of existing XTCE documents. The attribute can easily be stripped from a 1.2 document for processing by a 1.1 compatible tool. A 1.1 tool using schema-based parsing will ignore the optional field, when updated with the 1.2 schema.