Fix `StandardErrorStreamLogTest`.

It tested the `StandardOutputStreamLog` instead of the
`StandardErrorStreamLog`.
Extend the readme.

The readme has only shown the status of the CI server, but there are
more important things that should be part of the readme.
Add support for EditorConfig.

I need a definition of the basic coding style. EditorConfig is an IDE
independent tool for this.
Use fixed versions for test dependencies.

These dependencies don't have to support a range because they are not
use by projects that depend on System Rules. Having a fixed version
makes the build more reliable because the version will not change with
a new release of a dependency.
More to TestWatcher from ExternalResource.
Add log-on-failure mode with tests.