Set version to 0.1.0-SNAPSHOT

In preparation for significant changes for the new
nexus-staging-maven-plugin.

See https://groups.google.com/d/msg/clojure-dev/lBpfII2u6vM/LQvr_rO5UGgJ
Add nexus-staging-maven-plugin for Sonatype OSS deploys
Update compiler and release plugin versions