Extract the template engine

[ghostbuster91]

Could you extract the template engine so it could be reused by other projects? I just created an adaptation of this plugin for gradle, and I am also plan to do one for android.

https://github.com/ghostbuster91/gradle-boilerplate

[jrudolph]

Sounds useful but not sure when I would get to it. I guess a PR would be welcome which splits the project into engine and sbt-plugin subproject.