Add coverage testing

.coveragerc

@@ -0,0 +1,36 @@
+[run]
+branch = True
+source =
+    src/sshecret
+    packages/sshecret-admin/src/sshecret_admin
+    packages/sshecret-backend/src/sshecret_backend
+    packages/sshecret-sshd/src/sshecret_sshd
+
+omit =
+    */__init__.py
+    */types.py
+    */testing.py
+    */settings.py
+    */main.py
+    */cli.py
+    */tests/*
+    */test_*.py
+    */conftest.py
+    */site-packages/*
+concurrency = multiprocessing
+
+[report]
+show_missing = True
+skip_covered = True
+
+exclude_lines =
+    if __name__ == .__main__.:
+    def __repr__
+    def __str__
+    def __eq__
+    def __ne__
+    raise NotImplementedError
+    except ImportError
+
+[html]
+directory = coverage_html_report