compiler plugin jar size sprawl

[matanox]

The compiler plugin jar has grown to around 1MB, mainly composed of dependency jars from the canve-shared project. I think many of them can be discluded either through sbt-assembly or by sbt's exclude part of the libraryDependencies DSL (a commented example of which can be seen in the current build.sbt).

We should not include unnecessary libraries in the compiler plugin's uberjar, as each one of them can be a source of entanglement for collision with user versions of the same, or exotic sbt bugs that come into play around it all. Not to mention small size means faster downloads, which also matters.

Shared infrastructure is important, but a clean healthy distributable jar is a higher goal.

Feedback from the github-cruncher may be used to research possible problems before touching this.