Simplify the gemspec
Switch the Rakefile to use Bundler rather than Jeweler
Remove outdated "discover" functionality
Clean up the gemfile and test setup
Assume Active Model is present as a runtime dependency
Clean up the license
Remove Jeweler's old VERSION file
Clean up and expand the changelog

This uses the Gemnasium changelog conventions as outlined in:
https://github.com/tech-angels/vandamme/tree/v0.0.7#changelogs-convention
Clean up the readme, updating the RSpec example
Ruby 1.8 hash syntax
Use Bundler's default .gitignore
Add separate gemfiles for testing each minor Active Model version
Test against each new gemfile
Notifications are sent by default
Add support for Ruby 2.1
Allow Travis build failure on EOL'd Rubies