Update Rails 4.2 version for tests
undefined variable warning
Reverse order of modules in test

This currently triggers an error. Because of the order in which the
scopes are build, the "scope" column ends up on the "restaurants" table
rather than the slugs table. I'm making the change in the test to ensure
that the next commit fixes the problem.
Update the where condition for scope in scope_for_slug_generator in the History module.

This prevents an ActiveRecord::StatementInvalid: Mysql2::Error: Unknown
column '<table_name>.scope' exception
Don't test deprecated finds on AR 4.2+
Skip reserved candidates
Updated Changelog
Add byebug to development dependencies
Fix friendly finds on Rails 4.2

Rails has done its usual song and dance and changed the way Model.find
works in 4.2, so it's now no longer delegated to the internal relation
class, but is its own method, so we solve this by including the finders
module in the model class as well as the relation class.

Resolves #607
Bump version
Link to issues in Changelog

[ci skip]
Move byebug to Gemfile

Otherwise it causes the build to error out on JRuby and RBX.
Updated README for 5.1