Use Rails4

Task 13274
Make add_index method work with Rails4

Task 13274
Make test migrations pass

Task 13274
Build schema.rb with rails4

Task 13274
Make specs pass with rails4

Task 13274
Address deprecation warnings

Task 13274
Update README with note about rails 3

Task 13274
Update travis settings

Task 13274
Fix typos, formatting

Task 13274
Task 13319
Merge TMXCredit/pg_power#45 v2.0.0 'origin/13274_rails4_new'

Task 13274
Task 13319

* origin/13274_rails4_new:
  Fix typos, formatting
  Update travis settings
  Update README with note about rails 3
  Address deprecation warnings
  Make specs pass with rails4
  Build schema.rb with rails4
  Make test migrations pass
  Make add_index method work with Rails4
  Use Rails4