1.4.0-RC1 is a temporary release to test all of the changes that have
happened since 1.3.4 and 1.3.5. It fixes many bugs, improves overall
performance and adds support for user-facing features such as debugging and
the experimental "offloading compilation from sbt".
If everything goes well after Christmas, 1.4.0 will be released. Release
notes for the final release will be exhaustive and will include all changes
happened since v1.3.4.