Added CHANGELOG to repository

Following up on the discussion in the scala-ide-dev ML
(http://groups.google.com/group/scala-ide-dev/browse_thread/thread/97e05f5ab17ebfc7/ee2251ba5c5aa53f#ee2251ba5c5aa53f),
added a CHANGELOG to the repository.
Update CHANGELOG

Added a CHANGELOG item for the pull request you already accepted.
Merge pull request #271 from mads379/patch-1

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Updated CHANGELOG
Update CHANGELOG
Merge pull request #272 from sschaef/issue/changelog-update

Update CHANGELOG