sbt-release + sbt-sonatype support

[aishfenton]

Adding SBT plugins that make releases easier.

Running sbt release does:

• Runs tests
• Tags the release (which means it goes into the releases section on github)
• Automates the tedious Maven central / Sonatype release process
• Increments version.sbt

New process is also documented in CONTRIB.md.

Also added Roger as author in POM.xml file :)

[aishfenton]

Needs to be merged with Travis-CI before build will stop failing.

[dbtsai]

LGTM except minor new line.