(SERVER-120) Update CHANGELOG for 0.4.0 release notes

Contains changelog updates for the release summary.
Merge pull request #266 from nwolfe/svr120-release-notes

(SERVER-120) Update CHANGELOG for 0.4.0 release notes
Merge pull request #265 from nwolfe/svr120-update-version-number

(SERVER-120) Update version to 0.4.0 for release
(SERVER-120) Bump version to SNAPSHOT