Changes for Zthes XML DTD, version 0.5

Changes between versions 0.3b and 0.5:

• The previous version rather stupidly only allowed a single term to be represented in a document. In practice, documents with multiple terms were made simply by jamming together multiple valid documents into a single invalid one. Version 0.5 requires each term to be wrapped in a <term>...</term> pair, so there may be arbitrarily many of them.