* Allow for ignoring unmerged branches using a regular expression. Use the `branches_to_ignore` option to specify a
regular expression, like this:
`subversion = metric_source.Subversion()
product = domain.Product(project, name='Product', short_name='PR',
metric_source_ids={subversion: 'http://svn/trunk/foo/'},
metric_options={metric.UnmergedBranches: dict(branches_to_ignore_re='feature.*')})`