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.

setup.py

@@ -0,0 +1,23 @@
+import re
+import sys
+from setuptools import setup
+
+print_warning = False
+m = re.search(r'^VERSION\s*=\s*\'v(\d\.\d\.\d)\'', open('src/ssh_audit/ssh_audit.py').read(), re.M)
+if m is None:
+    # If we failed to parse the stable version, see if this is the development version.
+    m = re.search(r'^VERSION\s*=\s*\'v(\d\.\d\.\d-dev)\'', open('src/ssh_audit/ssh_audit.py').read(), re.M)
+    if m is None:
+        print("Error: could not parse VERSION variable from ssh_audit.py.")
+        sys.exit(1)
+    else:  # Continue with the development version, but print a warning later.
+        print_warning = True
+
+version = m.group(1)
+print("\n\nPackaging ssh-audit v%s...\n\n" % version)
+
+# see setup.cfg
+setup()
+
+if print_warning:
+    print("\n\n    !!! WARNING: development version detected (%s).  Are you sure you want to package this version?  Probably not...\n" % version)