textgraph 1.1.0

added functionality to save and load textgraph topic objects
added functionality to visualize rwr terms
added functionality for explore_topics(): open result without saving it; print top terms as table; different output formats
added the option to calculate document relevance in calculate_dynamic_topics() and calculate_topics() as page rank in a document-document graph
performance increases in calculate_dynamic_topics() and calculate_topics() via data.table implementation
bug fixes in calculate_dynamic_topics(), calculate_topics(), classify_documents(), explore_topics()
fixed erroneous widyr version requirement

textgraph 1.0