task to init ENVied for Rails

task to generate the necessary files to use ENVied in a Rails project.

Takes care of a proper `ENVied.require` for:
* springified Rails project (`bin/rails console`)
* spring disabled (`DISABLE_SPRING=1 bin/rails console`)
* non-springified commands ('bin/rails server')

/cc @Odaeus @jewilmeer @haarts wanna testdive?