add codecov recommended coveragerc

Author: willingc

.coveragerc

@@ -1,2 +1,12 @@
 [run]
 source = bookstore
+
+[report]
+exclude_lines =
+    if self.debug:
+    pragma: no cover
+    raise NotImplementedError
+    if __name__ == .__main__.:
+ignore_errors = True
+omit =
+    */tests/*

tox.ini

@@ -61,4 +61,5 @@ basepython =
     dist: python3.6
     docs: python3.6
 deps = .[test]
-commands = pytest -v --maxfail=2 --cov=./ -W always
+commands =
+    pytest -v --maxfail=2 --cov=bookstore -W always