FLUME-2105. Add docs for MorphlineSolrSink.

(Wolfgang Hoschek via Mike Percy)
FLUME-2107. Update 1.4.0-SNAPSHOT to 1.4.0 for release.

(Mike Percy)
FLUME-2108. Update RELEASE-NOTES and CHANGELOG for 1.4.0 release.

(Mike Percy)
FLUME-2108. Corrections to CHANGELOG for 1.4.0 release.

(Mike Percy)