Fix some typos in CHANGELOG.
Merge pull request #663 from bernd/changelog-typos

Fix some typos in CHANGELOG
Allow empty plugin sections again.

This used to work with 1.1.x.

See: https://logstash.jira.com/browse/LOGSTASH-1344
Merge pull request #664 from bernd/LOGSTASH-1344

Allow empty plugin sections again (LOGSTASH-1344)
Merge git://github.com/logstash/logstash