Do not duplicate doctest setup
Do not require execution mode to be set in subflow activity

Defaults to SYNCHRONOUS.
Remove finished activity from activity before transitioning

This way at the moment of finished process there will be no "running"
activities in the process.  Previously, activities were removed during
recursion backtracking.
Show diffs in doctest failure messages
Subflow XPDL feature implemented

Current implementation supports synchronous execution only
Make sure activity ids are not reused by subflows
Process.startedSubflows considered useless
Refactor initSubflow to deal with ids for less dependencies
Changelog entry, version increment
Merge branch 'subflows'