Added support of sending A, B, C, and D as DTMF tones and uppercase W for a 1 second pause

We have added support of sending the characters A, B, C, and D as DTMF (Dual-Tone Multi-Frequency) tones to the products below:

• Digits attribute for <Play>
• sendDigits attribute for <Dial><Number>
• SendDigits parameter for the Call Resource 
• Digits within the Say/Play Widget in Studio
• Send digits within the Make Outgoing Call Widget in Studio

We have also added support of uppercase W for a 1 second pause between DTMF tones in addition to lowercase w which already produces a 0.5 second pause. 

For more information, please refer to the docs:

• TwiML™ Voice: <Play> | Twilio
• TwiML™ Voice: <Number> | Twilio
• Call Resource | Twilio
• Say/Play Widget | Twilio
• Make Outgoing Call Widget | Twilio
• What are DTMF Tones? | Twilio