Change CI to use pytest. Closes #103.

[coveralls]

Pull Request Test Coverage Report for Build 668653319

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 30 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+30.3%) to 89.85%

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Files with Coverage Reduction	New Missed Lines	%
wdreconcile/wikidatavalue.py	6	76.95%
tests/init.py	7	22.22%
wdreconcile/subfields.py	17	78.89%
<!--	Total:	30		-->

Totals
Change from base Build 668533559:	30.3%
Covered Lines:	1673
Relevant Lines:	1862

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💛 - Coveralls