4.0.0

Changelog from version 3.0.0 to 4.0.0:

33e0959 new version 4.0.0
afde939 new tests for KnowledgeGraph
636fb53 The Return of the Singleton
cab13d2 Improvint autocomplete and quit of terminal
867d4bb adding python demo
49c3fe6 setting more thread-safe functions for the knowledge_graph
89e7cdf new unit tests created
f210e95 moving template methods to header
b127c66 adding lock/mutex to update callback
d5476c3 new POO graph
a3adbd9 fixing export in core package