improve versioning code in build.sbt
travis: cache ~/.ivy2
build needs to be container based to use cache
setup publishing jars on tags
fix command for publishing jars
fix deploy section
fix directory structure of dist.zip
use sbt-sonatype plugin

- remove some other redundant publishing settings
add build status to README
allow travis to publish to sonatype
move publishSigned command
only need sonatype settings on the root

- adding it on other projects causes duplicate execution,
  breaking the sonatype* tasks
add sonatypeRelease to travis settings
enable publishing snapshot builds
update release info