Fix "the the"
Note Rails 4.x support in README
Update credits
Eliminate "should" from specs
Use explicit time format in db:dump_dir Rake task

The format of Time#to_s varies by Ruby version.
Refactor Rake tasks into a module
Add specs for Rake tasks
Merge pull request #70 from dnrce/rake-specs

Add specs for Rake tasks
Add a changelog

Closes #71

[ci skip]