[#5] Serve root as static when in development.

Configure server to serve root directory when in development, skipping
origin check. This allows the demos to be used, without further ado.
Note that it is not sufficient to serve `demo/`, as access is needed to
`src/`.

To view the rectangles demo in development, start the server and visit
</demo/rectangles/index.html>.
[#5] Document serving of root as static for development.
Merge branch 'feature/5-serve-static-dev' into develop