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.

snapcraft.yaml

@@ -0,0 +1,21 @@
+name: ssh-audit
+version: '2.2.0-1'
+license: 'MIT'
+summary: ssh-audit
+description: |
+  SSH server and client security configuration auditor.  Official repository: <https://github.com/jtesta/ssh-audit>
+
+base: core18
+grade: stable
+confinement: strict
+
+apps:
+  ssh-audit:
+    command: bin/ssh-audit
+    plugs: [network,network-bind]
+
+parts:
+  ssh-audit:
+    plugin: python
+    python-version: python3
+    source: .