Bump version to 2.3.0 (cloudevents#437)

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

[2.2] Bump version to 2.2.1 (cloudevents#438)

Run:
```
./mvnw versions:set -DnewVersion=2.2.1 -DgenerateBackupPoms=false -B
find . -type f -name "*.md" -exec sed -i -e "s+<version>[a-zA-Z0-9.-]*<\/version>+<version>2.2.1</version>+g" {} +
```

Signed-off-by: Pierangelo Di Pilato <pdipilat@redhat.com>

Bump to 2.2.0 (cloudevents#399)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.1.1 (cloudevents#390)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.1.0 (cloudevents#377)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.0.0 (cloudevents#343)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.0.0.RC2 (cloudevents#327)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.0.0-SNAPSHOT (cloudevents#310)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.0.0-milestone4 (cloudevents#254)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>

Bump to 2.0.0-milestone3 (cloudevents#246)

Signed-off-by: GitHub <noreply@github.com>

Co-authored-by: slinkydeveloper <slinkydeveloper@users.noreply.github.com>