v1.0.0

This release changes how settings are passed to the cors directive,
extracting them from the Actor System configuration if not provided (see #72).

Application code may use the new CorsSettings.apply functions instead of
the CorsSettings.defaultSettings to have more control over the source of the
configuration.

• Load settings from the current Actor System (#37, #72).
• Update akka-http to 10.1.12.
• Update Scala to 2.13.2.
• Use sbt-sonatype plugin for release.