Add support for XML fragments to the {{{xmlio}}} module, so that build output and reports don't need to be nested in a meaningless element (such as {{{<log type="distutils"><messages><message ...>}}}).

[sdist]
formats = bztar, gztar, zip

[unittest]
test-suite = bitten.tests
xml-results = build/test-results.xml
coverage-results = build/test-coverage.txt
coverage-dir = build/coverage