Rails 2.3.x compatibility patch.

Rails 2.3 doesn't have Engine support, so disable that and let people
add the helpers themselves via an initializer.

Based on @RyanNaughton's comments here:
https://github.com/andrew/split/issues/95
Add Rails 2.3 initialization steps to the README.
Merge pull request #167 from Scoutmob/rails2.3-compatibility

Rails 2.3 compatibility