Fixes broken Ruby 1.8 support, adds tests

* Adds switch in gemspec for ActiveSupport to allow the gem to be used with Ruby v1.8
* Adds gitignores for temporary files
* Corrects Bigcommerce branding in license file
* Removes version from README, improves wordwrap
* Adds Bundler gem tasks to Rakefile
* Adds Coveralls to gemspec for public code coverage
* Adds author details to gemspec
* Adds test for deprecation exception
* Adds Coveralls init to spec helper, with guard for Ruby prior to 1.9
* Updates RSpec mock api context to use `double` (`mock` is deprecated)
* Adds Ruby 2.0.0 and REE (1.8) versions to Travis CI config
* Bumps gem version to 0.8.3