Stringify IndexDefinition column names

* Other adapters construct IndexDefinitions from fetched strings
NullObject should respond to #to_a and return empty Array

because you code may containt code like this:
ActiveRecord::Base.connection.execute(query).to_a.flatten.first
require activesupport dependencies
Test on Ruby 2.0.0 on CI
Fix unquoted string in README example
use HTTPS for URL in gemspec
Merge pull request #44 from amarshall/patch-1

Test on Ruby 2.0.0 on CI
Merge pull request #48 from ktdreyer/gemspec-url

use HTTPS for URL in gemspec
Merge pull request #45 from amarshall/patch-3

Fix unquoted string in README example
Revert "Removed Jeweler from project"

This reverts commit 9ee3220271f4da408a51b33e3f915a46c5b26c1a.
Removed lockfiles
Updated .gitignore
Fixed test deprecations
Modified travis config: removed 1.9.2 and added 2.1.0
Add some travis sugar
Temporarily removed some build targets for faster test runs
Test gemfile update
Possible fix for ActiveRecord 2.3
Require activesupport for supporting MRI 2.0.0 and up
Remove old tasks and messages from Rakefile