Knowledgecore

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* added test for wildcard retracting
* wildcard retracting
allowing wildcards when retracting entries from the knowledge
base. E.g., retracting 'some_subj ?p ?o' will now delete any triplet
from the specified model in the knowledge base where the subject
is 'some_subj'.
* Contributors: Séverin Lemaignan, lorenzoferrini

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* add launch file
* Contributors: Séverin Lemaignan

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* add dependency on reasonable
* update pypi doc
* Contributors: Séverin Lemaignan

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* fix KB.find to properly handle ROS queries with no variable specified
It now returns all present variables instead of an error
* output literal as python/JSON literal instead of XSD ones
* minor debug msg changes
* Contributors: Séverin Lemaignan

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* add missing space in SPAQRL prefixes
* [api] expose 'stats' to the ROS py wrapper
* [minor] improve debug message experience
* Update README.md with example of how to use the ROS API
* increase logging level of several msgs
* fix corner case where trying to publish to unregistered evt topic
* Contributors: Séverin Lemaignan

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* [api] add (back) ability to save the knowledge base
* Contributors: Séverin Lemaignan