Updated version for next release cycle
Include additional instructions in Dockerfiles

Allows the insertion of additional Dockerfile instructions

The :instructions value is taken from the :uberimage options map
in project.clj and specifies a list of Dockerfile instructions to
be inserted immediately after the FROM instruction at the start
of the Dockerfile.
Updated project.clj, release notes and readme for 0.3.0
Merge release/0.3.0