Improve PyPI packaging (#71)

* Move files for better setup.py packaging

* Update setup.py and configs for src layout

* Run tests on setup.py build

In effect, this tests that the setup.py configuration is correct.

coverage combine and coverage:paths are added to keep the displayed
coverage paths as src/ssh_audit/*.py instead of
.tox/$envname/**/site-packages/ssh_audit/*.py

* Remove unnecessary encoding declarations

Python 3 defaults to UTF-8 encoding.
https://docs.python.org/3/reference/lexical_analysis.html#encoding-declarations

* Remove shebang from colorama type stubs

Shouldn't need to be an executable.
Related: git has this file tracked as chmod -x.

Makefile.pypi

@@ -0,0 +1,11 @@
+all:
+	python3 setup.py sdist bdist_wheel
+
+uploadtest:
+	twine upload --repository-url https://test.pypi.org/legacy/ dist/*
+
+uploadprod:
+	twine upload dist/*
+
+clean:
+	rm -rf build/ dist/ src/*.egg-info/