Added azure core to common.

common/azure-storage-common.gemspec

common/lib/azure/core.rb

common/lib/azure/core/auth/authorizer.rb

common/lib/azure/core/auth/shared_key.rb

common/lib/azure/core/auth/shared_key_lite.rb

common/lib/azure/core/auth/signer.rb

common/lib/azure/core/default.rb

common/lib/azure/core/error.rb

common/lib/azure/core/filtered_service.rb

common/lib/azure/core/http/debug_filter.rb

common/lib/azure/core/http/http_error.rb

common/lib/azure/core/http/http_filter.rb

common/lib/azure/core/http/http_request.rb

common/lib/azure/core/http/http_response.rb

common/lib/azure/core/http/retry_policy.rb

common/lib/azure/core/http/signer_filter.rb

common/lib/azure/core/service.rb

common/lib/azure/core/signed_service.rb

common/lib/azure/core/utility.rb

common/lib/azure/core/version.rb