Py-trees

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* [behaviours] generators for variable values in SetBlackboardVariable, `300 <https://github.com/splintered-reality/py_trees/pull/300>`_

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* [composites] fix current_child problems on dynamic child insertion/removal, `289 <https://github.com/splintered-reality/py_trees/pull/289>`_

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* [blackboard] bugfix metadata not created on static set, `286 <https://github.com/splintered-reality/py_trees/pull/286>`_

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* [composites] parallel bugfix to invalidate correctly, `285 <https://github.com/splintered-reality/py_trees/pull/285>`_

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* [idioms] the either_or pattern, designed to replace the Chooser, `283 <https://github.com/splintered-reality/py_trees/pull/283>`_
* [behaviours] TickCounter, a timer based on tree ticks, `283 <https://github.com/splintered-reality/py_trees/pull/283>`_
* [behaviours] CheckBlackboardVariableValues, logical checks across multiple values, `283 <https://github.com/splintered-reality/py_trees/pull/283>`_
* [common] ComparisonExpression, a more concise way of storing checkers, `283 <https://github.com/splintered-reality/py_trees/pull/283>`_
* [composites] protect against adding a child to multiple parents, `281 <https://github.com/splintered-reality/py_trees/pull/281>`_

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* [blackboards] log a one-shot warning instead of exceptions when pickle fails, `156 <https://github.com/splintered-reality/py_trees_ros/pull/156>`_