Common configuration variables for authentication

[ab320012]

Issue Summary

in line with industry standards i added default authentication parameters to initialize the twilio client so for example if you initialize the configuration variables you will no longer need to add the auth token and sid in the code but can initialize the library with Twilio::REST::Client.new

I added a pr for this as well

Steps to Reproduce

PR #695

Code Snippet

# Your Account SID and Auth Token from console.twilio.com
#account_sid = "ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
# auth_token = "your_auth_token"
ENV['TWILIO_ACCOUNT_SID']
ENV['TWILIO_AUTH_TOKEN']


@client = Twilio::REST::Client.new

Exception/Log

# paste exception/log here

Technical details:

• twilio-ruby version: n/a
• ruby version: n/a

[manisha1997]

Hi @ab320012 , Can we have a link to any RFC that determines these industry standards, then we can take a look at it.
This way the application can pick up environment variables unknown to the user himself.