Changes Exceptions to Errors

[philnash]

• Moves twilio-ruby/framework/exception.rb to twilio-ruby/error.rb
  • This follows convention in other ruby libraries, I checked faraday, twitter and koala
• Errors inherit from StandardError instead of Exception
  • So that they can be caught by a plain rescue
• Errors renamed to reflect they are errors not exceptions
• Raising REST errors renamed to use Twilio::RestError and method name error, not exception
• Renames non-generated usage of Twilio::REST::TwilioException to Twilio::TwilioError

Note, the tests are horribly broken because the Twilio::REST::TwilioException is being tested for in every api call. This is generated code so will make an update to the code generator to fix this. This PR and the resultant update to the generator should be merged at the same time or things will be really broken.

[ghost]

Addressed in next-gen branch.

[philnash]

@tmconnors This PR was against the next-gen branch and I don't see a commit that does the equivalent. I noticed that the generator now tests for Twilio::REST::TwilioError. Do you need me to update this PR to make the error class exist within the Twilio::REST module?