Don't force developers to use a specific Ruby

...but allow them to pin the version themselves.
Merge pull request #76 from zoombody/rails-support

Clarify Rails version support
Merge pull request #77 from zoombody/ruby-version

Don't force developers to use a specific Ruby
Updating changelog, releasing 1.5.2
Remove preloader 'nodoc' call
Update safe_yaml decency to a more conservative option
Dependency is on rails 4.1 now, update preloader calls
Target both Rails 4.0 and 4.1
Use older preloader syntax for Rails 4 compat