use semantic versioning

Use version numbers that follow MAJOR.MINOR.PATCH as specified in by
semantic versioning (https://semver.org/).

CONTRIBUTING.md

@@ -64,10 +64,9 @@ Here is an [Example](https://github.com/cucumber/bool/pull/12) of this process i
 ### Do a release
 
 - Release commit (e.g. [fdf8a5c](https://github.com/cucumber/cucumber-cpp/commit/fdf8a5c4ef4c51dfa7ea82077f706414a4c6322d)):
-  - Change `CHANGELOG.md` renaming the "In Git" section with the
-    release number and date
-  - Commit with message `Update changelog for the X.Y release`
-  - Create an annotated tag for this commit named `vX.Y`
+  - Change `CHANGELOG.md` renaming the "In Git" section with the release number and date
+  - Commit with message `Update changelog for the X.Y.Z release`
+  - Create an annotated tag for this commit named `vX.Y.Z`
 - New development branch commit (e.g. [da60995](https://github.com/cucumber/cucumber-cpp/commit/da609956fcd42046e5182c6226acd7e53dd7754e)):
   - Add new "In Git" section to `CHANGELOG.md`
   - Commit with message `Preparing history file for next development release`