scala 3.0.0-RC1 milestone

Finished sweep through book examples, before the M4 release

Bumped the examples version

Bumped the version, added a milestone for M3

More fully uses the new Scala 3 syntax

Bumped version to 2.5.0

Updated the README

Added acknowledgment for oldbig's contribution of Maven support. Adde…

…d a note about a known Specs2 issue.

Merge pull request deanwampler#22 from deanwampler/scala-212-213

Now supports 2.13.0-RC2

Merge remote-tracking branch 'refs/remotes/origin/master'