Update copyright years in the LICENSE file.
Optimize logo.png.
Start 2.1.0 development.
Change minimum Rails version to 4.0.0.
Add notes about installing gems for page/action caching.
Simplify test application.
Fix tests on Rails 4.1.0.
Improve monkey patching in engine.rb.

It is now less likely to need to change the monkey patching code in
engine.rb if Rails changes the code it replaces.
Remove empty lines at the end of all remaining files.
Add Gemfile.
Update .gitignore files.
Add mailmap.
Replace secret_token with secret_key_base.
Remove the hack in engine.rb.

It doesn't seem to be required in 4.0.0 and above.