Add final remark to issue #60. Last problem is finally fixed.
Add register_as() to simplify replacing formatter implementations (if necessary).
Tweak min-duration threshold handling.
Plain formatter prints now multi-line step parts (text/doc-string, table).
Refactor out common parts to behave.model_describe (and reuse them).
Adapt pretty formatter accordingly.
Show now multi-line step parts (text, table) in XML output.
Change output to improve readability in XML file (complete scenario).
Change output related to step failures slightly.
Use all behave4cmd0 steps now.
Provide basic checks for exploratory testing.
Add self-test when feature file contains more than one feature.
Add description for latest changes.