Add a simple web server with the `-w` flag.
Add the observer and handler to the server.
Normalize the user's provided site path.

Handling an individual file highlighted an inconsistency in how the site path
was passed in. Remove any trailing path separator so things are always the
same.
Add a development server to listen for changes.
Test that the development server is served.
Add documentation about the server.
Fix Python 3 support.
Adjust NOQA to skip Python 3 missing import coverage.
coverage is "pragma: no cover", not "NOQA."
Merge pull request #22 from mblayman/devserver

Add a development server.