new: initial support for multiprocessing & concurrency

[aMahanna]

• Introducing enable_rich as an optional constructor parameter to disable progress bars. Defaults to True.
• Wrapping create_collection() and create_graph() operations with a try/except for thread handling
• Add test_pgt_concurrent for an example of how to use ArangoRDF with ThreadPoolExecutor
• Add .rst file for concurrency support
• Add .rst file for ArangoDB to RDF transformations

[coveralls]

Pull Request Test Coverage Report for Build 19933975384

Details

• 86 of 89 (96.63%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 94.712%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
arango_rdf/utils.py	21	22	95.45%
arango_rdf/main.py	65	67	97.01%

Totals
Change from base Build 18635306213:	-0.003%
Covered Lines:	1182
Relevant Lines:	1248

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💛 - Coveralls